U.S. patent application number 12/966499 was filed with the patent office on 2011-04-07 for method and system for detecting electrophysiological changes in pre-cancerous and cancerous tissue and epithelium.
This patent application is currently assigned to EPI-SCI, LLC. Invention is credited to Richard J. Davies.
Application Number | 20110082358 12/966499 |
Document ID | / |
Family ID | 37215303 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110082358 |
Kind Code |
A1 |
Davies; Richard J. |
April 7, 2011 |
METHOD AND SYSTEM FOR DETECTING ELECTROPHYSIOLOGICAL CHANGES IN
PRE-CANCEROUS AND CANCEROUS TISSUE AND EPITHELIUM
Abstract
A method and system for determining a condition of a selected
region of epithelial and stromal tissue, for example in the human
breast. A plurality of electrodes are used to measure surface and
transepithelial electropotential of breast tissue as well as
surface electropotential and impedance at one or more locations and
at several defined frequencies, particularly very low frequencies.
An agent may be introduced into the region of tissue to enhance
electrophysiological characteristics. Measurements made at ambient
and varying suction and/or positive pressure applied to the
epithelial tissue and/or positive pressure conditions applied to
the breast are also used as a diagnostic tool. Tissue condition is
determined based on the electropotential and impedance profile at
different depths of the epithelium, stroma, tissue, or organ,
together with an estimate of the functional changes in the
epithelium due to altered ion transport and electrophysiological
properties of the tissue. Devices for practicing the disclosed
methods are also provided.
Inventors: |
Davies; Richard J.; (Saddle
River, NJ) |
Assignee: |
EPI-SCI, LLC
Saddle River
NJ
|
Family ID: |
37215303 |
Appl. No.: |
12/966499 |
Filed: |
December 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11409144 |
Apr 21, 2006 |
7853319 |
|
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12966499 |
|
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60673448 |
Apr 21, 2005 |
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Current U.S.
Class: |
600/382 ;
600/547 |
Current CPC
Class: |
A61B 5/0538 20130101;
A61B 5/6834 20130101; A61B 5/053 20130101; A61B 5/4312
20130101 |
Class at
Publication: |
600/382 ;
600/547 |
International
Class: |
A61B 5/053 20060101
A61B005/053; A61B 5/04 20060101 A61B005/04 |
Claims
1. A method for determining a condition of a region of epithelial
or stromal tissue comprising: A. measurement of an impedance
spectrum over a region of tissue where an abnormality is suspected
(suspicious region); B. measurement of an impedance spectrum over a
region of tissue where no abnormality is suspected (control
region); C. application of mechanical pressure or compression over
the suspicious region; D. measurement of the impedance spectrum in
the suspicious region following the application of mechanical
pressure; E. application of mechanical pressure or compression over
the control region; F. comparison of the impedance profile before
and after compression in the suspicious region; G. comparison of
the impedance profile before and after compression in the control
region; and H. comparison of the impedance profile of the
suspicious region to the control region.
2. A computer-readable medium having computer-executable
instructions for performing a method for determining the presence
of a tumor in the human breast comprising: establishing a
connection between a first electrode and a region of epithelial
tissue within the duct of a breast; establishing a connection
between a second electrode on the surface of the breast;
establishing a signal between the first and second electrodes;
measuring an electrical property between the first and second
electrode; applying at least one form of pressure to at least one
region of the breast, the form pressure selected from the group
consisting of positive pressure, negative pressure and a
combination of positive and negative pressure; measuring an
electrical property between the first and second electrode in
response to the pressure; and determining the presence of a tumor
based on the signal, or the change in the signal in response to the
pressure, between the first and second electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of
U.S. Provisional Patent Application No. 60/673,448 filed Apr. 21,
2005, the disclosure of which is hereby incorporated herein by
reference. This application is a continuation of U.S. application
Ser. No. 11/409,144, filed on Apr. 21, 2006, the disclosure of
which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the detection of
abnormal or cancerous tissue, and more particularly, to the
detection of changes in the electrophysiological characteristics of
abnormal or cancerous tissue and to changes in those
electrophysiological characteristics related to the functional,
structural and topographic (the interaction of shape, position and
function) relationships of the tissue during the development of
malignancy. These measurements are made in the absence and presence
of pharmacological and hormonal agents to reveal and accentuate the
electrophysiological characteristics of abnormal or cancerous
tissue.
[0003] Cancer is a leading cause of death in both men and women in
the United States. Difficulty in detecting abnormal pre-cancerous
or cancerous tissue before treatment options become non-viable is
one of the reasons for the high mortality rate. Detecting of the
presence of abnormal or cancerous tissues is difficult, in part,
because such tissues are largely located deep within the body, thus
requiring expensive, complex, invasive, and/or uncomfortable
procedures. For this reason, the use of detection procedures is
often restricted until a patient is experiencing symptoms related
to the abnormal tissue. Many forms of cancers or tumors, however,
require extended periods of time to attain a detectable size (and
thus to produce significant symptoms or signs in the patient). It
is often too late for effective treatment by the time the detection
is performed with currently available diagnostic modalities.
[0004] Breast cancer is the most common malignancy affecting women
in the Western World. The reduction in mortality for this common
disease depends on early detection. The mainstay of early detection
are X-ray mammography and clinical breast examination. Both are
fraught with problems of inaccuracy. For example, mammography has a
lower sensitivity in women with dense breasts, and is unable to
discriminate between morphologically similar benign or malignant
breast lesions.
[0005] Clinical breast examinations are limited because lesions
less than one cm are usually undetectable and larger lesions may be
obscured by diffuse nodularity, fibrocystic change, or may be too
deep in the breast to enable clinical detection. Patients with
positive mammogaphic or equivocal clinical findings often require
biopsy to make a definitive diagnosis. Moreover, biopsies may be
negative for malignancy in up to 80% of patients.
[0006] Accordingly, mammography and clinical breast examination
have relatively poor specificity in diagnosing breast cancer.
Therefore many positive mammographic findings or lesions detected
on clinical breast examination ultimately prove to be false
positives resulting in physical and emotional trauma for patients.
Improved methods and technologies to identify patients who need to
undergo biopsy would reduce healthcare costs and avoid unnecessary
diagnostic biopsies.
[0007] Other technologies have been introduced in an attempt to
improve on the diagnostic accuracy attainable with mammography and
clinical breast examination alone. Breast ultrasound is helpful in
distinguishing between cystic or solid breast lesions and may be
useful in guiding needle or open biopsies. However, such techniques
are unable to determine whether a solid mass, or calcifications are
benign or malignant. Magnetic resonance imaging has been introduced
in an attempt to improve on the accuracy of mammography. Its high
cost and low specificity limit its general applicability for
diagnosing and screening for breast cancer. Nuclear imaging with
Positron Emission Tomogaphy (PET) has a lower sensitivity for small
lesions, but is limited by cost.
[0008] It is also desirable to develop improved technology suitable
for diagnosing pre-cancerous tissue and cancer in other tissue
types and elsewhere in the body, particularly methods and devices
suitable for ascertaining the condition of bodily ductal
structures, e.g., the prostate, pancreas, etc., as well as the
breast.
[0009] One proposed method for early detection of cancerous and
pre-cancerous tissue includes measuring of the electrical impedance
of biological tissue. For example, U.S. Pat. No. 3,949,736
discloses a low-level electric current passed through tissue, with
a measurement of the voltage drop across the tissue providing an
indirect indication of the overall tissue impedance. This method
teaches that a change in impedance of the tissue is associated with
an abnormal condition of the cells composing the tissue, indicating
a tumor, carcinoma, or other abnormal biological condition. This
disclosure, however, does not discuss either an increase or
decrease in impedance associated with abnormal cells, nor does it
specifically address tumor cells.
[0010] The disadvantage of this and similar systems is that the DC
electrical properties of the epithelium are not considered. Most
common malignancies develop in an epithelium (the cell layer that
lines a hollow organ, such as the bowel, or ductal structures such
as the breast or prostate), that maintains a transepithelial
electropotential. Early in the malignant process the epithelium
loses its transepithelial potential, particularly when compared to
epithelium some distance away from the developing malignancy. The
combination of transepithelial electropotential measurements with
impedance are more accurate in diagnosing pre-cancerous and
cancerous conditions.
[0011] Another disadvantage of the above referenced system is that
the frequency range is not defined. Certain information is obtained
about cells according to the range of frequencies selected.
Different frequency bands may be associated with different
structural or functional aspects of the tissue. See, for example,
F. A. Duck, Physical Properties of Tissues, London: Academic Press,
2001; K. R. Foster, H. P. Schwan, Dielectric properties of tissues
and biological materials: a critical review, Crit. Rev. Biomed.
Eng., 1989, 17(1): 25-104. For example at high frequencies such as
greater than about 1 GHz molecular structure has a dominating
effect on the relaxation characteristics of the impedance profile.
Relaxation characteristics include the delay in the response of a
tissue to a change in the applied electric field. For example, an
applied AC current results in voltage change across the tissue
which will be delayed or phase shifted, because of the impedance
characteristics of the tissue. Relaxation and dispersion
characteristics of the tissue vary according to the frequency of
the applied signal.
[0012] At lower frequencies, such as less than about 100 Hz, or the
so called .alpha.-dispersion range, alterations in ion transport
and charge accumulations at large cell membrane interfaces dominate
the relaxation characteristics of the impedance profile. In the
frequency range between a few kHz and about 1 MHz, or the so-called
.beta.-dispersion range, cell structure dominates the relaxation
characteristics of the epithelial impedance profile. Within this
range at low kHz frequencies, most of the applied current passes
between the cells through the paracellular pathway and tight
junctions. At higher frequencies in the .beta.-dispersion range the
current can penetrate the cell membrane and therefore passes both
between and through the cells, and the current density will depend
on the composition and volume of the cytoplasm and cell nucleus.
Characteristic alterations occur in the ion transport of an
epithelium during the process of malignant transformation affecting
the impedance characteristics of the epithelium measured at
frequencies in the .alpha.-dispersion range. Later in the malignant
process, structural alterations with opening of the tight junctions
and decreasing resistance of the paracellular pathways, together
with changes in the composition and volume of the cell cytoplasm
and nucleus, affect the impedance measured in the .beta.-dispersion
range.
[0013] Another disadvantage with the above referenced system is
that the topography of altered impedance is not examined. By
spacing the measuring electrodes differently the epithelium can be
probed to different depths. The depth that is measured by two
surface electrodes is approximately half the distance between the
electrodes. Therefore electrodes 1 mm apart will measure the
impedance of the underlying epithelium to a depth of approximately
500 microns. It is known, for example, that the thickness of bowel
epithelium increases at the edge of a developing tumor to
1356.+-.208.mu. compared with 716.+-.112.mu. in normal bowel. D.
Kristt, et al. Patterns of proliferative changes in crypts
bordering colonic tumors: zonal histology and cell cycle marker
expression. Pathol. Oncol. Res 1999; 5(4): 297-303. Thickening of
the ductal epithelium of the breast is also observed as ductal
carcinoma in-situ develops. By comparing the measured impedance
between electrodes spaced approximately 2.8 mm apart and compared
with the impedance of electrodes spaced approximately 1.4 mm apart,
information about the deeper and thickened epithelium may be
obtained. See, for example, L. Emtestam & S. Ollmar. Electrical
impedance index in human skin: measurements after occlusion, in 5
anatomical regions and in mild irritant contact dermatitis. Contact
Dermatitis 1993; 28(2): 104-108.
[0014] Another disadvantage of the above referenced methods is that
they do not probe the specific conductive pathways that are altered
during the malignant process. For example, potassium conductance is
reduced in the surface epithelium of the colon early in the
malignant process. By using electrodes spaced less than 1 mm apart
with varying concentrations of potassium chloride the potassium
conductance and permeability may be estimated in the surface
epithelium at a depth from less than 500.mu. to the surface.
[0015] A number of non-invasive impedance imaging techniques have
been developed in an attempt to diagnose breast cancer. Electrical
impedance tomography (EIT) is an impedance imaging technique that
employs a large number of electrodes placed on the body surface.
The impedance measurements obtained at each electrode are then
processed by a computer to generate a 2 dimensional or 3
dimensional reconstructed tomographic image of the impedance and
its distribution in 2 or 3 dimensions. This approach relies on the
differences in conductivity and impedivity between different tissue
types and relies on data acquisition and image reconstruction
algorithms which are difficult to apply clinically.
[0016] The majority of EIT systems employ "current-driving mode,"
which applies a constant AC current between two or more
current-passing electrodes, and measures the voltage drop between
other voltage-sensing electrodes on the body surface. Another
approach is to use a "voltage-driving approach," which applies a
constant AC voltage between two or more current-passing electrodes,
and then measures the current at other current-sensing electrodes.
Different systems vary in the electrode configuration, current or
voltage excitation mode, the excitation signal pattern, and AC
frequency range employed.
[0017] Another disadvantage with using EIT to diagnose breast
cancer is the inhomogeneity of breast tissue. The image
reconstruction assumes that current passes homogeneously through
the breast tissue which is unlikely given the varying electrical
properties of different types of tissue comprising the breast. In
addition image reconstruction depends upon the calculation of the
voltage distribution on the surface of the breast from a known
impedance distribution (the so called forward problem), and then
estimating the impedance distribution within the breast from the
measured voltage distribution measured with surface electrodes (the
inverse problem). Reconstruction algorithms are frequently based on
finite element modeling using Poisson's equation and with
assumptions with regard to quasistatic conditions, because of the
low frequencies used in most EIT systems.
[0018] Other patents, such as U.S. Pat. Nos. 4,955,383 and
5,099,844, disclose that surface electropotential measurements may
be used to diagnose cancer. Empirical measurements, however, are
difficult to interpret and use in diagnosis. For example, the above
referenced inventions diagnose cancer by measuring voltage
differences (differentials) between one region of the breast and
another and then comparing them with measurements in the opposite
breast. Changes in the measured surface potential may be related to
differences in the impedance characteristics of the overlying skin.
This fact is ignored by the above referenced and similar
inventions, resulting in a diagnostic accuracy of 72% or less. J.
Cuzick et al. Electropotential measurements as a new diagnostic
modality for breast cancer. Lancet 1998; 352(9125): 359-363; M.
Faupel et al. Electropotential evaluation as a new technique for
diagnosing breast lesions. Eur. J. Radiol. 1997; 24 (1): 33-38.
Neither AC impedance, or surface DC measurement approaches, measure
the transepithelial breast DC potential or AC impedance
characteristics of the breast epithelium.
[0019] Other inventions that use AC measurement, such as U.S. Pat.
No. 6,308,097, also have a lower accuracy than may be possible with
a combination of DC potential measurements and AC impedance
measurements, that also measure the transepithelial electrical
properties of mammary epithelium. Electrical impedance scanning
(EIS) also known as electrical impedance mapping (EIM) avoids the
limitations of complex image reconstruction encountered with EIT.
The above referenced system diagnoses cancer by only measuring
decreased impedance (increased conductance) and changes in
capacitance over a cancer. It does not measure the mammary
transepithelial impedance characteristics of the breast. There are
several other limitations to this approach. Inaccuracies may occur
because of air bubbles. Underlying bones, costal cartilages, muscle
and skin may result in high conductance regions, which produce
false positives. Depth of measurement is limited to 3-3.5 cm, which
will result in false negatives for lesions on the chest wall. It is
also not possible to localize lesions using this approach.
[0020] Another potential source of information for the detection of
abnormal tissue is the measurement of transport alterations in the
epithelium. Epithelial cells line the surfaces of the body and act
as a barrier to isolate the body from the outside world. Not only
do epithelial cells serve to insulate the body, but they also
modify the body's environment by transporting salts, nutrients, and
water across the cell barrier while maintaining their own
cytoplasmic environment within fairly narrow limits. One mechanism
by which the epithelial layer withstands the constant battering is
by continuous proliferation and replacement of the barrier. This
continued cell proliferation may partly explain why more than 80%
of cancers are of epithelial cell origin. Moreover, given their
special abilities to vectorially transport solutes from blood to
outside and vice versa, it appears that a disease process involving
altered growth regulation may have associated changes in transport
properties of epithelia.
[0021] It is known that the addition of serum to quiescent
fibroblasts results in rapid cell membrane depolarization. Cell
membrane depolarization is an early event associated with cell
division. Depolarization induced by growth factors appears biphasic
in some instances but cell division may be stimulated without
depolarization. Cell membrane depolarization is temporally
associated with Na.sup.+ influx, and the influx persists after
repolarization has occurred. Although the initial Na.sup.+ influx
may result in depolarization, the increase in sodium transport does
not cease once the cell membrane has been repolarized, possibly due
to Na/K ATPase pump activation. Other studies also support the
notion that Na.sup.+ transport is altered during cell activation.
In addition to altered Na.sup.+-transport, K.sup.+-, and
Cl.sup.--transport is altered during cell proliferation.
[0022] A number of studies have demonstrated that proliferating
cells are relatively depolarized when compared to those that are
quiescent or non-dividing. Differentiation is associated with the
expression of specific ion channels. Additional studies indicate
that cell membrane depolarization occurs because of alterations in
ionic fluxes, intracellular ionic composition and transport
mechanisms that are associated with cell proliferation.
[0023] Intracellular Ca.sup.2+ (Ca.sup.2+.sub.i) and pH (pH.sub.i)
are increased by mitogen activation. Cell proliferation may be
initiated following the activation of phosphatidylinositol which
releases two second messengers, 1,2-diacylglycerol and
inosotol-1,4,5-triphosphate, which triggers Ca.sup.2+.sub.i release
from internal stores. Ca.sup.2+.sub.i and pH.sub.i may then alter
the gating of various ion channels in the cell membrane, which are
responsible for maintaining the voltage of the cell membrane.
Therefore, there is the potential for interaction between other
intracellular messengers, ion transport mechanisms, and cell
membrane potential. Most studies have been performed in transformed
and cultured cells and not in intact epithelia during the
development of cancer.
[0024] It was known for some time that cancer cells are relatively
depolarized compared with non-transformed cells. It has been
suggested that sustained cell membrane depolarization results in
continuous cellular proliferation, and that malignant
transformation results as a consequence of sustained depolarization
and a failure of the cell to repolarize after cell division. C. D.
Cone Jr., Unified theory on the basic mechanism of normal mitotic
control and oncogenesis. J. Theor. Biol. 1971; 30(1): 151-181; C.
D. Cone Jr., C. M. Cone. Induction of mitosis in mature neurons in
central nervous system by sustained depolarization. Science 1976;
192(4235): 155-158; C. D. Cone, Jr. The role of the surface
electrical transmembrane potential in normal and malignant
mitogenesis. Ann. N.Y. Acad. Sci. 1974; 238: 420-435. A number of
studies have demonstrated that cell membrane depolarization occurs
during transformation and carcinogenesis. Other studies have
demonstrated that a single ras-mutation may result in altered ion
transport and cell membrane depolarization. Y. Huang, S. G. Rane,
Single channel study of a Ca(2+)-activated K+ current associated
with ras induced cell transformation. J. Physiol. 1993; 461:
601-618. For example, there is a progressive depolarization of the
colonocyte cell membrane during 1,2 dimethylhydrazine (DMH)-induced
colon cancer in CF.sub.1 mice. The V.sub.A (apical membrane
voltage) measured with intracellular microelectrodes in
histologically "normal" colonic epithelium depolarized from -74.9
mV to -61.4 mV after 6 weeks of DMH treatment and to -34 mV by 20
weeks of treatment. The cell membrane potential in a benign human
breast epithelial cell line (MCF-10A) was observed to be -50.+-.4
mV (mean.+-.SEM) and was significantly depolarized at -35.+-.1 mV
(p<0.002) in the same cell line after ras-transformation (the
MCF-10AT cell line).
[0025] While epithelial cells normally maintain their intracellular
sodium concentration within a narrow range, electronmicroprobe
analysis suggests that cancer cells exhibit cytoplasmic
sodium/potassium ratios that are three to five times greater than
those found in their non-transformed counterparts. These
observations partly explain the electrical depolarization observed
in malignant or pre-malignant tissues, because of the loss of
K.sup.+ or Na.sup.+ gradients across the cell membrane.
[0026] In addition to cell membrane depolarization, and altered
intracellular ionic activity, other studies have shown that there
may be a decrease in electrogenic sodium transport and activation
of non-electrogenic transporters during the development of
epithelial malignancies. These changes may affect or occur as a
consequence of altered intracellular ionic composition.
[0027] In addition to cell membrane depolarization, and altered
intracellular ionic activity, other studies have shown that there
may be a decrease in electrogenic sodium transport and activation
of non-electrogenic transporters during the development of
epithelial malignancies. These changes may occur as a consequence
of altered intracellular ionic composition. Other specific ion
transport alterations have been described in colon, prostate,
breast, uterine cervix, melanoma, urothelium, and pancreas during
proliferation, differentiation, apoptosis, and carcinogenesis.
[0028] Apoptosis or physiological cell death is down-regulated
during the development of malignancy. Ion transport mechanisms
affected by apoptosis include the influx of Ca.sup.2+,
non-selective Ca.sup.2+-permeable cation channels,
calcium-activated chloride channels, and
K.sup.+--Cl.sup.--cotransport. J. A. Kim et al. Involvement of Ca2+
influx in the mechanism of tamoxifen-induced apoptosis in Hep2G
human hepatoblastoma cells. Cancer Lett. 1999; 147(1-2): 115-123;
A. A. Gutierrez et al. Activation of a Ca2+-permeable cation
channel by two different inducers of apoptosis in a human prostatic
cancer cell line. J. Physiol. 1999; 517 (Pt. 1): 95-107; J. V.
Tapia-Vieyra, J. Mas-Oliva. Apoptosis and cell death channels in
prostate cancer. Arch. Med. Res. 2001; 32(3): 175-185; R. C. Elble,
B. U. Pauli. Tumor Suppression by a Proapoptotic Calcium-Activated
Chloride Channel in Mammary Epithelium. J. Biol. Chem. 2001;
276(44): 40510-40517.
[0029] Loss of cell-to-cell communication occurs during
carcinogenesis. This results in defective electrical coupling
between cells, which is mediated via ions and small molecules
through gap junctions, which in turn influences the electrical
properties of epithelia.
[0030] Epithelial cells are bound together by tight junctions,
which consist of cell-to-cell adhesion molecules. These adhesion
proteins regulate the paracellular transport of molecules and ions
between cells and are dynamic structures that can tighten the
epithelium, preventing the movement of substances, or loosen
allowing substances to pass between cells. Tight junctions consist
of integral membrane proteins, claudins, occludins and JAMs
(junctional adhesion molecules). Tight junctions will open and
close in response to intra and extracellular stimuli.
[0031] A number of substances will open or close tight junctions.
The proinflammatory agent TGF-alpha, cytokines, IGF and VEGF opens
tight junctions. Zonula occludens toxin, nitric oxide donors, and
phorbol esters also reversibly open tight junctions. Other
substances close tight junctions including calcium, H2 antagonists
and retinoids. Various hormones such as prolactin and
glucocorticoids will also regulate the tight junctions. Other
substances added to drug formulations act as non-specific tight
junction modulators including chitosan and wheat germ
agglutinin.
[0032] The above referenced substances and others may act directly
or indirectly on the tight junction proteins, which are altered
during carcinogenesis. For example claudin-7 is lost in breast
ductal epithelium during the development of breast cancer. The
response of the tight junctions varies according to the malignant
state of the epithelium and their constituent proteins. As a result
the opening or closing of tight junctions is affected by the
malignant state of the epithelium.
[0033] Polyps or overtly malignant lesions may develop in a
background of disordered proliferation and altered transepithelial
ion transport. Experimental animal studies of large bowel cancer
have demonstrated that transepithelial depolarization is an early
feature of the pre-malignant state. In nasal polyp studies, the
lesions had a higher transepithelial potential, but these lesions
were not pre-malignant in the same sense as an adenomatous or
pre-malignant colonic polyp, that are usually depolarized.
Electrical depolarization has been found in biopsies of malignant
breast tissue. Recently alterations in impedance have been found to
be associated with the pre-malignant or cancerous state in breast
and bowel.
[0034] It has been discovered that transepithelial depolarization
was a specific event associated with colonic carcinogenesis in
CF.sub.1 mice. The more susceptible site, the distal colon,
underwent about a 30% decrease in transepithelial potential
(V.sub.T) after only four weeks of carcinogen treatment. This was
before histological changes developed. A non-specific cytotoxic
agent (5-fluorouracil), administered over the same period did not
cause a reduction in V.sub.T in the same model. The reduction in
V.sub.T was confirmed in a subsequent study where almost a 60%
reduction was observed after carcinogen treatment. It has also been
discovered that, although V.sub.T is invariably higher when
measured in vivo, the "premalignant" colonic epithelium is usually
depolarized when compared to normal colon.
[0035] DC electrical potential alterations have been used to
diagnose non-malignant conditions such as cystic fibrosis, cancer
in animal models, human cells or tissue and in man. Differences in
impedance between normal tissue and cancer have been described in
animal models in vitro human tissue in vitro and have been applied
to in vivo cancer diagnosis.
[0036] DC potential measurements have not been combined with
impedance measurements to diagnose cancer because the
electrophysiological alterations that accompany the development of
cancer have not been well understood or fully characterized.
Surface measurements of potential or impedance are not the same as
measurements performed across the breast epithelium, and described
below, where electrical contact is made between the luminal surface
of the duct and the overlying skin. Transepithelial depolarization
is an early event during carcinogenesis, which may affect a
significant region of the epithelium (a "field defect"). This
depolarization is accompanied by functional changes in the
epithelium including ion transport and impedance alterations. Early
on in the process these take the form of increased impedance
because of decreased specific electrogenic ion transport processes.
As the tumor begins to develop in the pre-malignant epithelium,
structural changes occur in the transformed cells such as a
breakdown in tight junctions and nuclear atypia. The structural
changes result in a marked reduction in the impedance of the tumor.
The pattern and gradient of electrical changes in the epithelium
permit the diagnosis of cancer from a combination of DC electrical
and impedance measurements.
[0037] Another reason that DC electropotential and impedance
measurements have not been successfully applied to cancer diagnosis
is that transepithelial potential and impedance may be quite
variable and are affected by the hydration state, dietary salt
intake, diurnal or cyclical variation in hormonal level or
non-specific inflammatory changes and other factors. In the absence
of knowledge about the physiological variables which influence
transepithelial potential and impedance these kind of measurement
may not be completely reliable to diagnose pre-malignancy or
cancer.
[0038] Furthermore, a detailed understanding of the functional and
morphological alterations that occur during carcinogenesis permits
appropriate electrical probing for a specifically identified ion
transport change that is altered during cancer development. For
example knowledge that electrogenic sodium absorption is altered
during cancer development in breast epithelium permits the use of
sodium channel blockers (amiloride) or varying sodium concentration
in the ECM (electroconductive medium) to examine whether there is
an inhibitable component of sodium conductance. By varying the
depth of the measurement (by measuring the voltage drop across
differently space electrodes), it is possible to obtain topographic
and depth information about the cancerous changes in the
epithelium. Using a combination of low and high frequency sine
waves probing at different depths we are able to correlate the
functional and morphological (structural) changes at different
depths, with the impedance profile of the tissue.
[0039] The diagnostic accuracy of current technology using DC
electropotentials or impedance alone have significant limitations.
Sensitivity and specificity for DC electrical measurements in the
breast have been reported as 90% and 55% respectively and 93% and
65% for impedance measurements. This would result in an overall
diagnostic accuracy of between 72-79%, which is probably too low to
result in widespread adoption. The measurement of ductal
transepithelial DC potential, ductal transepithelial AC impedance
spectroscopy alone, or the combination of DC electrical potentials
and impedance spectroscopy will result in a diagnostic accuracy of
greater than 90%, which will lead to improved clinical utility.
[0040] Breast cancer is thought to originate from epithelial cells
in the terminal ductal lobular units (TDLUs) of mammary tissue.
These cells proliferate and have a functional role in the
absorption and secretion of various substances when quiescent and
may produce milk when lactating. Functional alterations in breast
epithelium have largely been ignored as a possible approach to
breast cancer diagnosis. Breast epithelium is responsible for milk
formation during lactation. Every month pre-menopausal breast
epithelium undergoes a "rehearsal" for pregnancy with involution
following menstruation. The flattened epithelium becomes more
columnar as the epithelium enters the luteal phase from the
follicular phase. In addition, duct branching and the number of
acini reach a maximum during the latter half of the luteal phase.
Just before menstruation apoptosis of the epithelium occurs and the
process starts over again unless the woman becomes pregnant.
[0041] Early pregnancy and lactation may be protective against
breast cancer because they result in a more differentiated breast
epithelium which is less susceptible to carcinogenic influences
whether estrogen or other environmental factors. It therefore seems
that differentiated breast epithelium is less likely to undergo
malignant change. Differentiated epithelium has a distinct apical
and basolateral membrane domain to enable it to maintain vectorial
transport function (the production of milk). In addition,
differentiated cells maintain a higher cell membrane potential to
transport various ions, lactulose and other substances in and out
of the duct lumen. In contrast, more proliferative epithelial cells
have depolarized cell membranes and are less able to maintain
vectorial ion transport. Recently the epithelial Na.sup.+ channel
(ENaC) and the cystic fibrosis transmembrane conductance regulator
(CFTR) have been identified in mammary epithelium and both
localized on the apical, or luminal side, of the epithelium. These
two transporters can be probed for by using amiloride, a blocker of
the ENaC, or by opening up Cl.sup.- channels regulated by CFTR
using cAMP.
[0042] For example, 20 .mu.M luminal amiloride depolarized the
transepithelial potential from -5.9.+-.0.5 mV (mean.+-.SEM) by
+3.1.+-.0.5 mV. Forskolin (10 .mu.M), which raises cAMP and opens
Cl.sup.- channels via the CFTR hyperpolarized the breast epithelium
by -2.2.+-.0.1 mV. These changes were accompanied by an increase
(17%) and subsequent decrease (19%) in transepithelial resistance
respectively. In transformed breast epithelium the ENaC is
down-regulated, whereas Cl.sup.- secretion may increase, similar to
observations reported for carcinoma of the cervix. Non-lactating
breast epithelium has relatively leaky tight junctions. This
results in a paracellular shunt current, which hyperpolarizes the
apical membrane of the epithelial cell. The larger the shunt
current the more hyperpolarized the apical membrane and therefore
the epithelium depolarizes since:
[0043] TEP=V.sub.BL=V.sub.A and i=TEP/R.sub.S; where
[0044] TEP=Transepithelial potential;
[0045] V.sub.BL=voltage of the basolateral membrane;
[0046] V.sub.A=voltage of the apical membrane;
[0047] i=shunt current; and
[0048] R.sub.S=paracellular (shunt) resistance.
[0049] Evidence that breast carcinogenesis may be associated with
functional incompetence of breast epithelium also comes from a
number of other sources. Some transgenic strains of mice have
defective lactation. The transgenic src mouse which develops
hyperplastic alveolar nodules, otherwise develops a normal mammary
tree but has defective lactation. The notch4 and TGF.beta.
transgenic mouse also demonstrate defective lactation. Cyclin D1
females have persistent lactation 6-9 months after weaning, and
TGF.alpha. mice, which have a defect in apoptosis and fail to
undergo epithelial regression develop hypersecretion. These data
suggest that there is a relationship between epithelial function
and genetic expression which affects proliferation and tumor
development.
[0050] Breast cysts occur in 7% of the female population and are
thought to develop in the TDLUs. Apocrine cysts have a higher
potassium content than simple cysts. Apocrine cysts may be
associated with the subsequent development of breast cancer. There
may therefore be a fundamental change in the epithelium at risk for
breast cancer development with a redistribution of electrolyte
content across the cell membrane resulting in altered cyst
electrolyte content and cell membrane depolarization. Although it
is commonly known that during lactation the breast transports
lactulose, proteins, fatty acids, immunoglobulins cholesterol,
hormones, ions and water across the ductal and lobular epithelium
and actively secretes milk, it is less widely appreciated that in
the non-pregnant and non-lactating state the breast, throughout
life exhibits excretory and absorptive function. The difference
between the lactating and the non-lactating breast being of degree
and the chemical constitution of the nipple duct fluid. Ductal
secretions have been analyzed to diagnose biological conditions of
the breast.
[0051] A number of approaches have been used to obtain ductal
fluid, including a suction cup to obtained pooled secretions;
nipple aspiration fluid (NAF), and more recently, cannulation of
one of the 6-12 ducts that open onto the nipple surface. Substances
and cells within the duct fluid may therefore be accessed to
identify abnormalities that may be associated with the diseased
state of the breast. One disadvantage of the above referenced
approaches is the difficulty in obtaining adequate NAF or lavage
fluid to perform analysis. Another disadvantage has been the
inability to identify or cannulate the ducts where an abnormality
in the fluid or cells may be identified.
[0052] Hung (U.S. Pat. No. 6,314,315) has suggested an electrical
approach to identify ductal orifices on the nipple surface. In that
disclosure it is taught that DC potential or impedance measurement
may facilitate the identification of openings or orifices on the
surface of the nipple. However, it is not taught that the
characteristics of the DC electrical signal or impedance may
characterize the condition of the breast. Moreover, it is not
taught that breast transepithelial DC measurements, transepithelial
AC impedance spectroscopy, alone or in combination may be used to
diagnose breast cancer.
[0053] Ionic gradients exist between the fluid secretions within
the breast ducts and the plasma. For example, it is known that the
nipple aspirate fluid has a sodium concentration [Na.sup.+] of
123.6.+-.33.8 mEq/l (mean.+-.standard deviation) compared with a
serum [Na.sup.+] of approximately 150 mEq/l (Petrakis1).
Nulliparous women have NAF [Na.sup.+] that are approximately 10
mEq/l higher than parous women, but still significantly below serum
levels. Similarly potassium concentration [K.sup.+] is
significantly higher at 13.5.+-.7.7 mEq/l in parous women and
12.9.+-.6.0 mEq/l in nulliparous women compared with serum levels
of [K.sup.+] of approximately 5.0 mEq/1. Other investigators have
reported lower NAF [Na.sup.+] of 53.2 mEq/l suggesting that
significant ionic gradients can be established between the plasma
and duct lumen in non-lactating breast. In pregnancy these
gradients are even higher for sodium with a [Na.sup.+] of
8.5.+-.0.9 mEq/l reported in milk which is almost 20 fold lower
than plasma. Chloride concentration [Cl.sup.-] in milk is almost
one tenth of the concentration found in plasma with values of
11.9.+-.0.5 mM reported. Although [Na.sup.+] and [Cl.sup.-] levels
in ductal secretions rise and the [K.sup.+] falls following the
cessation of lactation, significant ionic gradients are maintained
between the duct lumen and plasma.
[0054] Furthermore, in women undergoing ovulatory cycles during
lactation distinct changes have been observed in the ion and
lactulose concentrations of breast milk. The first change occurs
5-6 days before ovulation and the second 6-7 days after ovulation.
During these periods [Na.sup.+] and [Cl.sup.-] increased more than
two-fold and [K.sup.+] decreased approximately 1.5-fold. It is
unclear whether changes in estrogen or progesterone levels before
and after ovulation are affecting the ion composition of milk.
However, it is known that alterations in the ionic composition of
milk influences the transepithelial electrical potential as
measured in mammals.
[0055] Furthermore, it is known that various hormones affect breast
epithelial ion transport. For example, prolactin decreases the
permeability of the tight-junctions between breast epithelial
cells, stimulates mucosal to serosal Na.sup.+ flux, upregulates
Na.sup.+:K.sup.+:2Cl.sup.- cotransport and increases the [K.sup.+]
and decreases the [Na.sup.+] in milk. Glucocorticoids control the
formation of tight-junctions increasing transepithelial resistance
and decreasing epithelial permeability. Administration of cortisol
into breast ducts late in pregnancy has been shown to increase the
[K.sup.+] and decrease [Na.sup.+] of ductal secretions.
Progesterone inhibits tight-junction closure during pregnancy and
may be responsible for the fluctuations in ductal fluid
electrolytes observed during menstrual cycle in non-pregnant women,
and discussed above. Estrogen has been observed to increase cell
membrane and transepithelial potential and may stimulate the
opening of K.sup.+-channels in breast epithelial cells. The
hormones mentioned above vary diurnally and during menstrual cycle.
It is likely that these variations influence the functional
properties of breast epithelium altering the ionic concentrations
within the lumen, the transepithelial potential and impedance
properties, which are dependent upon the ion transport properties
of epithelial cells and the transcellular and paracellular
conductance pathways.
[0056] Accordingly, these variations can be used as diagnostic
indicia of changes to breast tissue, which have to date yet to be
exploited. Thus, there remains a need for effective and practical
methods for detecting abnormal breast tissue as well as other
epithelial and/or ductal tissue.
[0057] The disclosures of the following patent applications, each
to Richard J. Davies, the inventor herein, are hereby incorporated
by reference herein: U.S. patent application Ser. No. 10/151,233,
filed May 20, 2002, entitled "Method and System for Detecting
Electrophysiological Changes in Pre-Cancerous and Cancerous
Tissue"; U.S. patent application Ser. No. 10/717,074, filed Nov.
19, 2003, entitled "Method And System For Detecting
Electrophysiological Changes In Pre-Cancerous And Cancerous Breast
Tissue And Epithelium"; and U.S. patent application Ser. No.
10/716,789, filed Nov. 19, 2003, entitled "Electrophysiological
Approaches To Assess Resection and Tumor Ablation Margins and
Responses To Drug Therapy".
SUMMARY OF THE INVENTION
[0058] One aspect of the invention provides a method for
determining a condition of a region of epithelial tissue, for
example epithelial breast tissue comprising: establishing a
connection between a first electrode and the epithelial tissue of
the nipple of a breast; placing a second electrode in contact with
the surface of the breast; establishing a signal between the first
and second electrodes; establishing that the nipple ducts of the
breast are open; measuring between the first and second electrode
(1) a DC potential; and (2) impedance at about 5 different
frequencies in the range of about 10 Hz to about 200 Hz and
impedance at from about 5 to about 50 different frequencies in the
range of about 0.1 Hz to about 10 Hz; and determining the condition
of the region of epithelial tissue based on the DC potential and
impedance measurements between the first and second electrode.
[0059] In another aspect of the invention there is provided a
method for determining a condition of a region of epithelial
tissue, for example, epithelial breast tissue comprising: placing
over the nipple of a breast a cup having an interior, and first and
second openings, and an electrode disposed within the interior, the
cup having a source of suction in communication with the first
opening, the second opening having been placed over the nipple;
establishing an electrical connection between the electrode and the
epithelial lining of the mammary ducts, which are in continuity
with the surface of the nipple of a breast through the duct
openings (orifices); placing a second electrode in electrical
contact with the surface of the breast; establishing a signal
between the first and second electrodes; establishing that the
nipple ducts of the breast are open; measuring a DC potential
between the first and second electrode; applying suction to the cup
sufficient to effect ductal collapse in a normal or non-malignant
duct; and measuring impedance at about 5 different frequencies in
the range of about 10 Hz to about 200 Hz and impedance at from
about 5 to about 50 different frequencies in the range of about 0.1
Hz to about 10 Hz; and altering the suction level and again
measuring impedance at about 5 different frequencies in the range
of about 10 Hz to about 200 Hz and impedance at from about 5 to
about 50 different frequencies in the range of about 0.1 Hz to
about 10 Hz; and determining the condition of the region of
epithelial tissue within the ducts and lobules of the breast, based
on the DC potential, and the impedance measurements under varying
pressure conditions.
[0060] In yet another embodiment of the invention there is provided
A method for determining a condition of a region of epithelial or
stromal tissue comprising: A. measurement of an impedance spectrum
over a region of tissue where an abnormality is suspected
(suspicious region); B. measurement of an impedance spectrum over a
region of tissue where no abnormality is suspected (control
region); C. application of mechanical pressure or compression over
the suspicious region; D. measurement of the impedance spectrum in
the suspicious region following the application of mechanical
pressure; E. application of mechanical pressure or compression over
the control region; F. comparison of the impedance profile before
and after compression in the suspicious region; G. comparison of
the impedance profile before and after compression in the control
region; and H. comparison of the impedance profile of the
suspicious region to the control region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate one embodiment
of the invention and together with the description, serve to
explain the principles of the invention.
[0062] FIG. 1 is a schematic diagram of a DC and AC impedance
measuring device, consistent with an embodiment of the present
invention;
[0063] FIG. 2 illustrates an exemplary embodiment of a device
suitable for use with systems and methods consistent with the
present invention;
[0064] FIG. 3 illustrates an exemplary embodiment of a surface
measurement probe suitable for use with systems and methods
consistent with the present invention;
[0065] FIG. 4 illustrates an exemplary embodiment of a nipple
electrode suitable for use with systems and methods consistent with
the present invention;
[0066] FIG. 5 illustrates an exemplary embodiment of a ductal
electrode probe suitable for use with systems and methods
consistent with the present invention;
[0067] FIG. 6 illustrates varying ionic content and the effect on
transepithelial conductance in human breast epithelium;
[0068] FIG. 7 illustrates measurements of cell membrane potential
in human breast epithelial cells;
[0069] FIG. 8 illustrates the effect of increasing estradiol
concentrations on the transepithelial potential in benign and
malignant breast epithelia;
[0070] FIG. 9 illustrates conductance and the electropotential
measurements made over the surface of the breast in women with and
without breast cancer;
[0071] FIG. 10 illustrates the measurement of electropotentials at
the surface of the breast, and variation of the measurement during
menstrual cycle;
[0072] FIG. 11 illustrates electrophysiological changes that occur
within the ductal epithelium during the development of breast
cancer;
[0073] FIG. 12 illustrates changes in the short circuit current of
human epithelium exposed to a potassium channel blocker (TEA) or
varying concentrations of potassium;
[0074] FIG. 13 illustrates how the information obtained in FIG. 12
may be used to plot the potassium gradient against the change in
short circuit current.
[0075] FIG. 14 illustrates multiple Nyquist impedance plots from
human breasts according to the present invention.
[0076] FIG. 15 illustrates the impedance profile for a patient with
a hemorrhagic cyst.
[0077] FIG. 16 illustrates a Bode plot of impedance data comparing
patients with fibrocystic disease (0465) and breast cancer
(0099).
[0078] FIG. 17 illustrates the same data as in FIG. 16 plotted as a
Nyquist plot.
[0079] FIG. 18 illustrates the impedance spectra data curve for
breast cancer tissue added to the curves of FIG. 17.
[0080] FIG. 19 illustrates the effects of altering the level of
suction applied to a nipple cup electrode on a normal breast.
[0081] FIG. 20 illustrates the effects of altering the level of
suction applied to a nipple cup electrode on a breast in which
malignancy is present.
[0082] FIG. 21 illustrates the method for estimating impedance for
the high suction curve associated with cancer in FIG. 20.
[0083] FIG. 22 illustrates the impedance profiles of a fibroadenoma
and carcinoma.
[0084] FIG. 23 illustrates the impedance profile of a normal duct
following compression.
[0085] FIG. 24 illustrates the same results as in FIG. 23 with an
expanded range for the X-axis.
[0086] FIG. 25 illustrates the impedance profile of a normal duct
following compression and release.
[0087] FIG. 26 illustrates the impedance profile of a breast cyst
following compression.
[0088] FIG. 27 illustrates the impedance profile following
compression of fibrocystic breast tissue.
[0089] FIG. 28 illustrates the impedance profile following
compression of fibroadenoma in breast tissue.
[0090] FIG. 29 illustrates the impedance profile following
compression of a more typical fibroadenoma in breast tissue.
DETAILED DESCRIPTION
[0091] Reference will now be made in detail to an embodiment of the
invention, an example of which is illustrated in the accompanying
drawings. Wherever possible, the same reference numbers will be
used throughout the drawings to refer to the same or like
parts.
[0092] The present invention overcomes problems and inadequacies
associated with prior methods used for characterizing abnormal or
cancerous epithelial tissue. In summary, various embodiments of the
present invention use DC and/or impedance measurements, under
ambient and/or variable suction, that pass the current or signal
across the breast epithelium and tumor using specially constructed
electrodes. For example a nipple electrode may be used to measure
the voltage and/or impedance between ductal epithelium, surrounding
breast tissue, skin and surface or other electrode. The nipple
electrode may also be used to pass the current along the ductal
system of the breast. Another type of electrode may be used to
measure the voltage and/or impedance signal, and/or pass a current
and measure the signal at the individual ductal orifices at the
nipple surface. Another type of electrode may be used to measure
the voltage and/or impedance signal, and/or pass a current and
measure the signal within individual ducts using a modified ductal
probe or ductoscope which may have one or more electrodes attached
to it. All of these electrodes may be used individually, in
combination with one another, or with a surface probe or
electrodes. Additionally DC and impedance measurements will be used
in combination to more adequately characterize abnormal or
cancerous tissues. DC measurements provide information about the
functional state of the epithelium and can detect early
pre-malignant changes and an adjacent malignancy. In particular,
impedance measurements at several frequencies in specifically
defined ranges using differently spaced electrodes provide depth
and topographic information to give both structural (high frequency
range) and functional (low frequency range) information about the
tissue being probed. Abnormal or cancerous tissue can be detected
and characterized by detecting and measuring transport alterations
in epithelial tissues, using ionic substitutions and/or
pharmacological and hormonal manipulations to determine the
presence of abnormal pre-cancerous or cancerous cells. A baseline
level of transepithelial DC potential, impedance or other
electrophysiological property that is sensitive to alterations in
transport in epithelia is measured in the tissue to be evaluated.
An agent may be introduced to enhance the transport or make it
possible to detect the transport alteration. The transepithelial DC
potential and/or impedance of the tissue (or other
electrophysiological property that may reflect or make it possible
to detect alterations in the transport) are then measured. Based on
the agent introduced and the measured electrophysiological
parameter, the condition of the tissue is determined.
[0093] A method and system are provided for determining a condition
of a selected region of breast epithelial tissue. At least two
current-passing electrodes are located in contact with a first
surface of the selected region of the tissue. Alternatively the
current passing electrodes may pass current across the tissue or
epithelium as for example between the nipple ducts, ductal lumen,
epithelium, breast parenchyma and surface of the breast.
Alternatively, the ducts may be accessed by a central duct catheter
or ductoscope. A plurality of measuring electrodes are located in
contact with the first surface of the breast as well. Initially,
one or more of the measuring electrodes is used to measure the DC
potential referenced to another electrode, or reference point. A
signal is established between the current-passing electrodes.
Impedance, associated with the established signal, is measured by
one or more of the measuring electrodes. Alternatively a
three-electrode system may be used for measurements whereby one
electrode is used for both current injection and voltage recording.
An agent is introduced into the region of tissue. The condition of
the tissue is determined based on the effect of the agent on
measured DC transepithelial potential, impedance or other
electrophysiological characteristic. The electrodes in the
described methods and apparatus can be used in contact with, in
proximity to, over, or inserted into the tissues being examined. It
should be understood that where the method is described in an
embodiment as encompassing one of these arrangements, it is
contemplated that it can also be used interchangeably with the
other. For example, where the method is described as having an
electrode in contact with the tissue, the method can also be used
with the electrode inserted into or in proximity to the tissue.
Similarly, where the method is described as having an electrode in
proximity to the tissue, it is contemplated that the electrode can
also be in contact with or inserted into the tissue.
[0094] In order to more accurately detect transport alterations in
abnormal pre-cancerous or cancerous epithelial tissue, a
pharmacological agent may be introduced to manipulate the tissue.
Pharmacological agents may include agonists of specific ion
transport and electrical activity, antagonists of specific ion
transport and electrical activity, ionic substitutions, and/or
hormonal or growth factor stimulation or inhibition of electrical
activity.
[0095] Depending on the location of the tissue to be investigated,
a number of methods may be used to administer the pharmacological
or hormonal agents. One exemplary method includes introducing the
agent directly to the tissue being investigated, via ductal
infusion, perfusion, direct contact or injection. Another exemplary
method includes applying the agent to the skin surface, wherein the
agent acts transcutaneously, or through the skin. Yet another
exemplary method includes electroporation, wherein the ductal
epithelium or surface is made permeable by the passage of
alternating current via electrodes in contact or penetrating the
organ or epithelium of interest. The agent then passive diffuses
into the organ and its constituent cells. The agent may be
introduced directly into the breast ductal system using the
modified nipple aspirator cup and electrode, or lavaged into a
specific duct using a ductal catheter or probe. Additional
exemplary methods include via inhalation, oral administration,
lavage, gavage, enema, parenteral injection into a vein or artery,
sublingually or via the buccal mucosa, or via intraperitoneal
administration. One skilled in the art will appreciate that other
methods are possible and that the method chosen is determined by
the tissue to be investigated.
[0096] Thus, systems and methods consistent with the present
invention use transepithelial electropotential or/and impedance
measurements to diagnose pre-malignancy or cancer. Further, systems
and methods consistent with the present invention use a defined set
of frequencies, in combination, to characterize functional and
structural alterations in pre-malignancy and cancer. By using
spaced electrodes the present invention may provide topographic and
geometrical (depth) information about the epithelium under
examination to diagnose pre-malignancy and cancer. In one
embodiment, systems and methods of the present invention use
electrodes with specially formulated ECMs to provide functional
information about the epithelium to diagnose pre-malignancy and
cancer.
[0097] In order to measure the transepithelial breast DC potential
it is necessary that the lumen of the duct be electrically accessed
by a nipple electrode constructed to make an electrical connection
between the Ag/AgCl (or similar low offset platinum/hydrogen,
titanium, tin-lead alloy, nickel, aluminum, zinc, carbon, or other
conductive metal or conductive polymer electrode) pellet recessed
within the nipple cup. The cup is filled with an ECM
(electro-conductive medium), which enters the ductal system
passively, or after aspiration with a syringe or pump, making
contact with the ductal lumen. A surface electrode placed at the
surface of the breast completes the electrical circuit, so that
measurements of transepithelial potential may be made between the
ductal epithelium, or center of the tumor and the skin surface.
Similar considerations have to be given to measure transepithelial
AC impedance whereby the measuring electrodes measure the voltage
drop and phase shift across the ductal epithelium or tumor, by
utilizing a nipple electrode in combination with a skin surface
electrode. Other configurations of this approach are more invasive,
whereby measurement can be made between an electrode inserted via a
ductoscope or nipple duct probe electrode referenced to the skin or
an IV (intravenous), intradermal, or subcutaneous electrode. In
another embodiment, the duct may also be accessed by a
needle-electrode inserted through the skin.
[0098] In order to combine DC transepithelial measurement with
impedance measurements, it is necessary to obtain baseline
measurement of the DC potential using the voltage sensing
electrodes, referenced to surface electrode with low-contact
impedance, or the blood stream via an IV, or the interstitial body
fluid via a needle electrode or electrode that permeabilizes the
overlying epidermis or other epithelium, or other body reference
point. The electrodes may contain different ionic concentrations,
pharmacological agents or hormones in their ECMs. As used in this
description, an ECM is a medium that permits transmission of
electrical signals between the surface being measured and the
electrode. An agent includes any ionic concentration,
pharmacological agent, hormone or other compound added to the ECM
or otherwise introduced to the tissue under investigation, selected
to provide further information about the condition of the tissue.
In another embodiment the concentrations of agents may be changed
using a flow through system.
[0099] Electroconductive media can include conductive fluids,
creams or gels used with external or internal electrodes to reduce
the impedance (resistance to alternating current) of the contact
between the electrode surface and the skin or epithelial surface.
In the case of DC electrodes it is also desirable that the ECM
results in the lowest DC offset at the electrode surface, or an
offset that can be measured. The ECM will often contain a hydrogel
that will draw fluid and electrolytes from deeper layers of the
skin to establish electrical contact with the surface electrode.
Electrodes that are used to pass current require ECMs with high
conductance. Usually this is accomplished by using ECMs with high
electrolyte content. The electrolytes frequently used are KCl
(potassium chloride) because of the similar ionic mobility of these
two ions in free solution, so that electrode polarization is less
of a problem than when ions of different mobility are used. Other
ions such as sodium may be used in ECM formulations, and the higher
electrolyte concentration result in more rapid electrode
equilibration.
[0100] In situations where estimations will be made of the
permeability of the epithelium to specific ions, the concentration
of K in the ECM will be varied so that the conductance of the
epithelium to potassium may be measured electrophysiologically. An
enhancer or permeant may be added to the ECM to increase the
conductance of the underlying skin to the electrolyte in the ECM.
Other approaches include mild surface abrasion with pumice and
alcohol to reduce surface skin resistance, abrasive pads such as
Kendall Excel electrode release liner (Tyco Health Care, Mansfield,
Mass.), 3M Red Dot Trace Prep (3M Corporation, St. Paul, Minn.),
cleaning the skin with alcohol, an automated skin abrasion
preparation device that spins a disposable electrode to abrade the
skin (QuickPrep system, Quinton, Inc., Bothell, Wash.), ultrasound
skin permeation technology (SonoPrep, Sontra Medical Corporation,
Franklin, Mass.), or silicon electrodes, which just penetrate the
stratum corneum to reduce skin surface resistance. (See also, the
comparison and discussion of several methods in Biomedical
Instrumentation & Technology, 2006; 39: 72-77; the content of
which is incorporated herein by reference.)
[0101] In order to measure the depth of the impedance alteration,
the voltage drop will be made between surface electrodes with
different spacing. Spacing will be determined by knowledge of the
depth to be probed. Similarly two different frequency ranges will
be used to measure functional and structural changes at different
depths.
[0102] In order to more accurately detect the functional transport
alterations at different depths in abnormal pre-cancerous or
cancerous epithelial tissue, a pharmacological agent is introduced
to manipulate the tissue, while electrically probing the tissue at
different frequencies and monitoring the voltage drop between
differently spaced electrodes. Pharmacological agents include
agonists of specific ion transport and electrical activity,
antagonists of specific ion transport and electrical activity,
ionic substitutions, and/or hormonal or growth factor stimulation
or inhibition of electrical activity.
[0103] Depending on the location of the tissue to be investigated,
a number of methods are used to administer the pharmacological or
hormonal agents. One exemplary method includes introducing the
agent directly to the tissue being investigated, via ductal
perfusion, infusion, direct contact or injection. Another exemplary
method includes applying the agent to the skin surface, wherein the
agent acts transcutaneously, or through the skin. Yet another
exemplary method includes electroporation, wherein the epithelium
or surface is made permeable by the passage of alternating current
via electrodes in contact or penetrating the surface of the breast
or ductal epithelium of interest. The agent then passively diffuses
into the breast and its constituent cells. Additional exemplary
methods include via inhalation, oral administration, lavage,
gavage, enema, parenteral injection into a vein or artery,
sublingually or via the buccal mucosa, or via intraperitoneal
administration. One skilled in the art will appreciate that other
methods are possible and that the method chosen is determined by
the tissue to be investigated.
[0104] Based on the agent introduced and the tissue being
investigated, measurements of electrophysiological properties, such
as impedance, are performed. Other properties that can be measured
includes, transepithelial potential, changes in spontaneous
oscillations in transepithelial potential or impedance associated
with the malignant state, time delay in a propagation signal
between electrodes, which indicates a loss of gap-junction
function. If adjacent cells are electrically coupled, one can
examine the loss of coupling by pharmacologically eliciting an
electrical signal and measuring the signal propagation up and
down-stream through surface epithelial cells. This is a functional
measurement of the gap-junctions, whereas simple electrical
stimulation will measure shunting of a current between the cells (a
structural measurement, at least in the high frequency range).
[0105] The results of these measurements are then used to determine
the condition of the investigated tissue. For example, research has
indicated that specific ion transport processes are altered during
the development of cancer. For example, a loss of electrogenic
Na.sup.+ transport, an up-regulation in Na/H exchange, a
down-regulation in K.sup.+ conductance, a decrease in basal
Cl.sup.- absorption, and a down-regulation in c-AMP (cyclic
adenosine-3',5'-cyclic monophosphate) stimulated Cl.sup.- secretion
have been observed.
[0106] Thus, by administering agents appropriate to the particular
epithelial tissue and measuring the associated electrophysiological
characteristics, it is possible to detect abnormal pre-cancerous or
cancerous tissue while the development of such tissue is at an
early stage. It should be understood that the method and system of
the present invention is applicable to any epithelial derived
cancer, such as, but not limited to, prostate, colon, breast,
esophageal, and nasopharyngeal cancers, as well as other epithelial
malignancies, such as lung, gastric, uterine cervix, endometrial,
skin and bladder.
[0107] Specifically, in cancers affecting mucosal or epithelial
tissues, transport alterations may be sufficiently large to suggest
that they are a consequence of an early mutation, affecting a large
number of cells (i.e., a field defect). In this case, they may be
exploited as potential biomarkers for determining which patients
should be either more frequently monitored, or conversely, may be
used to identify particular regions of epithelium that require
biopsy. The latter is especially helpful in the case of atypical
ductal hyperplasia or ductal carcinoma in situ (DCIS), which are
more difficult to detect mammographically, or by clinical breast
examination without having to resort to an invasive biopsy.
[0108] Applying the methods of the present invention, several
observations have been made:
[0109] (1) Differences in the total impedance are observed when
comparing malignant breasts with benign or normal breasts. The
total impedance is higher comparing malignant to benign breasts
with the total impedance exceeding 50,000 ohms, or even higher, for
the malignant breasts.
[0110] (2) Total capacitance was lower overall, comparing malignant
with benign or normal breasts.
[0111] (3) The impedance curves for normal and malignant breasts
separate at lower frequencies.
[0112] (4) The shape of the curves differs depending on the
pathological condition of the breast.
[0113] (5) Electrical resistance of the tumor may be lower at lower
frequencies, for example, in the range of about 1 to about 0.1
hertz. This also depends on the type and size of the tumor.
[0114] (6) Capacitance of the tumor may be higher at the lower
frequencies. This also depends on the pathological type and size of
the tumor.
[0115] (7) Differences exist between phase angle, characteristic
capacitance and the suppression of the center of the impedance arc
depending on the pathological status of the breast.
[0116] (8) When current is passed across a malignant tumor from
another site on the breast or body, rather than from the nipple to
the surface of the breast, the impedance may be lower when the
voltage drop is measured across the tumor rather than between the
nipple and the tumor i.e., across ductal epithelium. The
capacitance is usually higher when the measurement is made across a
malignant tumor, rather than across the ductal epithelium.
Therefore a combination of measurements; nipple to breast surface
(transepithelial impedance spectroscopy), body surface to breast
surface (transtumor impedance), and transepithelial potential
(ductal epithelium in series with skin provides the optimum
diagnostic information.
[0117] The methods of the present invention are particularly useful
when use is made of the entire frequency range between about 60,000
Hertz and about 0.1 Hertz, although most of the discriminatory
information is observed at frequencies below about 200 Hz. The
preferred protocol is to take 5-10 electrical measurements
(impedance, reactance, phase angle, resistance, etc.) between about
60,000 Hz and about 200 Hz and then take as many measurements as
possible (taking into consideration, for example, the comfort of
the patient, response time of the equipment, etc.) between about
200 and about 0.1 Hz; preferably between about 150 Hz and about 0.1
Hz; more preferably about 100 Hz and about 0.1 Hz; for example
between about 50 Hz and about 0.1 Hz. In practice, this can mean
taking about 20 to about 40 measurements in one or more of the
lower frequencies ranges.
[0118] It has also been observed that the application of
alternating suction and release opens up the nipple ducts so that
impedances are generally lower if this protocol is followed. This
will typically lower the impedance in the high frequency range.
This reduces measurement noise and enhances current passage along
the ducts to the tumor site. Further improvement can be made in
lowering the impedance of the nipple and larger collecting ducts by
using alcohol or a dekeratinizing agent such as Nuprep.RTM. to
remove keratin plugs in the surface duct openings on the nipple
surface. Methods for opening up the ductal system are known for
ductoscopy (e.g., Acueity), obtaining nipple aspirate fluid (NAF)
or ductal lavage (e.g., CYTYC), but this technology has not
previously been applied to the field of the present invention. A
particularly improved device will employ an automated suction pump
connected to a manometer to suction rhythmically, analogous to a
breast pump, then employ a holding suction pressure at a
predetermined level and then change the holding pressure to another
level so that the effect of altered suction on the impedance
spectra can be used as a diagnostic test. Without wishing to be
bound by theory, it is believed that a difference in electrical
response, for example a different impedance curve, arises due
ductal collapse with the application of suction in a normal breast
whereas the presence of malignancy in a duct inhibits such
collapse.
[0119] Mechanical pressure can also be used to provide additional
diagnostic information during DC and AC impedance measurement to
characterize breast tissue. In this manner, positive pressure is
applied to the skin surface and negative pressure, or vacuum is
applied to the nipple. In this manner an additional approach can be
used to obtain further diagnostic information that can be
independently used or can be used in combination with the technique
relating to nipple aspiration.
[0120] Two patterns of impedance and open circuit potential have
been observed from transepithelial impedance spectroscopy and DC
measurements in patients with benign or malignant breast lesions.
FIG. 22 demonstrates one source of false positives that can occur
with a low impedance fibroadenoma (a benign lesion). Two patterns
exist in the impedance spectral profile of breast cancer. The first
change is an increase in impedance, particularly at low frequency.
Without wishing to be bound by theory, this is believed due to the
ducts becoming packed with tumor cells (ductal-carcinoma in-situ,
DCIS) which increases the resistance of the ductal epithelium. Once
an invasive carcinoma and mass lesion develops within a duct
system, the tight-junctions between cells break down, resulting in
a decrease in impedance, particularly at low frequencies. In FIG.
22 the open circles demonstrate the impedance spectra of a control
ductal system in a patient with a carcinoma of the breast in a
quadrant of the breast that is uninvolved by tumor. It can be seen
that the open circles on the right side of the graph form a second
circular arc (Cole plot) that extends beyond the right side
vertical Y-axis. This indicates that a high impedance ductal system
exists in the control quadrant of this patient's breast. In the
opposite quadrant of the same patient's breast a mass has
developed. The impedance spectrum of that breast quadrant is
depicted by the open squares. The second semicircular arc has now
been replaced by a low impedance Cole plot that passes below the
X-axis. Since we have previously observed that the low frequency
impedance arc appears to be dominated by the terminal ducts, it is
likely that the terminal ducts have become less electrically
resistant in the region of the developing cancer. This suggests a
lower electrical impedance at this stage in the development of the
cancer.
[0121] In another patient the impedance spectra over a suspicious
mass appears similar to the developing cancer. This lesion had an
impedance spectra depicted by filled squares. The impedance curve
has lost its low impedance curve similar to the developing cancer.
The patient underwent a biopsy, the results of which demonstrated
that the mass was a benign fibroadenoma. Several features do
however distinguish the developing cancer from the
fibroadenoma:
[0122] (1) The middle part of the impedance arc is flattened in the
fibroadenoma (filled squares) compared with the carcinoma (open
squares);
[0123] (2) The notch frequency occurs at about 30 Hz for cancer
(this may occur as low as 1 Hz in cancer) and about 100 Hz for the
fibroadenoma. Notch frequency is the frequency at which there
appear two separate RC time-constants in the impedance spectra
resulting in two incompletely fused arcs. It is the frequency at
which the two arcs or double humps appear to partly separate. (See
Jossinet et al., Ann. NY Acad. Sci. 1999; 873: 30-41, incorporated
herein by reference.) The acronym RC stands for Resistor-Capacitor.
The product RC is referred to in the art as the time constant, and
is a characteristic quantity of an RC circuit. For example, when
t=RC, the capacitor has charged to a fraction equal to 1-1/e, or
about 63% of its final value. Typically the units of RC are seconds
or milliseconds. When the time constant of the high frequency RC
components of the circuit have a significantly different time
constant compared to the low frequency RC components, the resulting
figure exhibits two separate semi-circles on a Nyquist plot. If the
time constants are close to one another, the semi-circles will
appear to be fused. With better separation, in other words time
constants that differ more, the information obtained is more
diagnostically useful. As described above, a greater degree of
diagnostic information in the present invention is obtained in the
low frequency range; and
[0124] (3) The subepithelial resistance (the intercept of the
high-frequency impedance curve with the x-axis on the left side of
the curve) is much lower in the fibroadenoma (140 ohms) than in the
cancer (420 ohms).
[0125] As noted above, an alternative approach that can be used to
identify abnormalities in the breast and distinguish benign from
malignant disease involves the application of mechanical pressure
or compression to occlude the ductal pathway and thereby increase
the impedance pathway for the passage of electrical current through
the breast. The application of mechanical pressure or compression,
in other words positive pressure (in contrast with the application
of vacuum to, e.g., nipple ducts as described elsewhere herein),
can be accomplished by various means well-known to the skilled
practitioner. For example, one or more fingers or the hand can be
used to palpate an area of the breast, including a suspicious area
or an adjoining area thereto. Alternatively, a mechanical device,
such as a pressure transducer, can be used to apply a finite or
defined degree of pressure to a specific area. Additionally, the
use of mechanical pressure can be combined with the use of suction
or vacuum as described above. For convenience, the use of
mechanical pressure can be referred to as the mechanical pressure
protocol and it can be accomplished by one or more of the following
steps in the suggested order or in other sequences:
[0126] (1) Measurement of an impedance spectrum over a region of
tissue where an abnormality is suspected (suspicious region).
[0127] (2) Measurement of an impedance spectrum over a region of
tissue where no abnormality is suspected (control region).
[0128] (3) The application of mechanical pressure or compression
over the suspicious region.
[0129] (4) The measurement of the impedance spectrum in the
suspicious region following the application of mechanical
pressure.
[0130] (5) The application of mechanical pressure or compression
over the control region.
[0131] (6) The comparison of the impedance profile before and after
compression in the suspicious region.
[0132] (7) The comparison of the impedance profile before and after
compression in the control region.
[0133] (8) The comparison of the impedance profile of the
suspicious region to the control region.
[0134] (9) Using 6, 7 and 8 alone or in combination to diagnose the
normal or diseased state of the tissue.
[0135] (10) Measurement of the kinetics of the change in impedance
when pressure is applied or released over a region of tissue.
[0136] (11) Using the kinetics of the change in impedance to
diagnose the normal or diseased state of the tissue.
[0137] (12) Using a combination of a single or multiple pressure
transducer with steps 3-11 to obtain both a pressure profile, and
an impedance profile.
[0138] (13) Using a combination of the applied pressure profile
with the changes in the impedance profile to diagnose the normal or
diseased state of the tissue.
[0139] (14) Using a combination of the 1-13 with changes in the
suction pressure applied to the nipple-sensor aspirator-cup.
[0140] (15) Using a combination of the altered impedance profile
following changes in the applied suction pressure to the
nipple-sensor aspirator-cup with steps 1-13 to diagnose the normal
or diseased state of the tissue.
[0141] Ducts containing tumor will generally be less compliant, and
therefore less compressible than normal ducts not filled with tumor
cell. This is depicted in FIG. 23. The open squares depict the
impedance spectra of a normal duct which appears to have at least
two time constants. The notch frequency (the point at which the two
impedance curves incompletely fuse) in this normal duct is at about
4 Hz. When a pressure of up to 1 kgcm.sup.2 was applied over the
breast surface electrode a new impedance spectrum was measured at
59 frequencies logarithmically spaced between 60,000 Hz and 0.1 Hz
(filled squares). The impedance of the low frequency curve (below 4
Hz) is markedly increased due to occlusion of the more compliant
duct. In contrast, there is virtually no effect on the impedance
curve above 4 Hz. FIG. 24 demonstrates the effect on a large scale
of the X-axis. Note that the impedance increases from approximately
7850 ohms to almost 42,000 ohms. The open squares (no compression)
are obscured by the closed squares (compression).
[0142] FIG. 25 depicts the release of compression on the duct (open
circles) with the return of the impedance profile almost to control
(pre-compression) levels. Note that the kinetics and shape of the
release curve has specific characteristics in normal as opposed to
abnormal tissue. For example, the return of the impedance curve
takes several minutes due to the compliance properties of the
ductal and surrounding parenchymal tissue. These properties can be
used to characterize the pathological state of the tissue.
[0143] FIG. 26 demonstrates the same protocol applied to a cyst.
The open square QOI2:00 (quadrant of interest at the 2:00 o'clock
position) depicts the impedance spectrum over a cyst. When pressure
is applied (closed square) the impedance decreases, as may be
expected as the current pathway is decreased because of a decrease
in the anterior-posterior diameter of the cyst with compression.
The control quadrant is depicted by open circles, which pass off
the scale. A large cyst is expected to have a lower impedance than
the surrounding tissue because it conducts electricity better.
[0144] FIG. 27 demonstrates the same protocol applied to a region
of fibrocystic disease. Since the cystic component is minimal i.e.,
there is a more non-compliant fibrous element in this example,
there is a minimal effect observed with compression.
[0145] FIG. 28 demonstrates the same fibroadenoma shown in FIG. 22.
This fibroadenoma has a significantly lower impedance than is
usually observed and the lesion can be confused with a carcinoma.
The same pressure protocol was applied and an increase of impedance
was identified although less than that observed in a normal duct
(FIG. 24 and FIG. 25). It should be noted that the surrounding
ductal structure is less disrupted in a fibroadenoma than in
carcinoma and therefore some compression of the ductal structure
was possible. The same compression protocol applied to the
carcinoma in FIG. 22 results in no appreciable change in the
impedance profile, apparently because the ducts have already been
disrupted by the tumor and are less compressible.
[0146] FIG. 29 depicts a more typical fibroadenoma where the
impedance is higher. The control quadrant (open circles) has a
somewhat noisy impedance curve, but shows two partially fused RC
curves because of normal ductal structure. In this case the
pressure protocol results in minimal change in the impedance
spectrum. As has been demonstrated, the application of pressure in
combination with the electrical measurements described in detail
above to selected regions of the breast exhibiting suspicious
tissue can be used effectively to distinguish between malignant and
other types of abnormal tissue.
[0147] A number of variations are possible for devices to be used
with the present invention. Further, within a device design, there
are a number of aspects that may be varied. These variations, and
others, are described below.
[0148] One probe or other device includes a plurality of
miniaturized electrodes in recessed wells. Disposable commercially
available silicon chips processing functions, such as filtering,
may perform surface recording and initial electronic processing.
Each ECM solution or agent may be specific to the individual
electrode and reservoir on the chip. Thus, for one measurement, a
particular set of electrodes is used. For another measurement, for
example, at a different ionic concentration, a different set of
electrodes is used. While this produces some variations, as the
electrodes for one measurement are not located at the same points
as for another, this system provides generally reliable
results.
[0149] An alternative approach is to use fewer electrodes and use a
flow-through or microfluidic system to change solutions and agents.
Specifically, solutions or agents are changed by passing small
amounts of electrical current to move solution or agent through
channels and out through pores in the surface of the probe. In this
embodiment, the electrode remains in contact with the same region
of the skin or ductal epithelium, thus eliminating region-to-region
variation in measurement. This approach requires time for
equilibration between different solutions.
[0150] In detecting the presence of abnormal pre-cancerous or
cancerous breast tissue, a hand-held probe is provided for
obtaining surface measurements at the skin. The probe may include
electrodes for passing current as well as for measuring. An
impedance measurement may be taken between the nipple cup electrode
and the hand-held probe, or may be taken between electrodes on the
hand-held probe. Alternatively, a ductoscopic or non-optical ductal
probe may be interfaced with one or more miniaturized electrodes.
After taking initial DC measurements, a wetting/permeabilizing
agent may be introduced to reduce skin impedance or one of the
methods described hereinabove may be used. The agent may be
introduced using a microfluidic approach, as described above, to
move fluid to the surface of the electrodes. Alternatively, surface
electrodes that just penetrate the stratum corneum may be used to
decrease impedance.
[0151] Regardless of the configuration of the device, FIG. 1 is a
schematic of a DC and AC impedance measurement system 100 used in
cancer diagnosis, consistent with the present invention. The system
100 interfaces with a probe device 105 including multiple
electrodes, wherein the actual implementation of the probe device
105 depends on the organ and condition under test. The probe device
105 may incorporate the electrodes attached to a needle, body
cavity, ductoscopic, non-optical ductal or surface probe. A
reference probe 110 may take the form of an intravenous probe, skin
surface probe, nipple-cup or ductal epithelial surface reference
probe depending on the test situation and region of breast under
investigation.
[0152] To avoid stray capacitances, the electrodes may be connected
via shielded wires to a selection switch 120 which may select a
specific probe 105 following a command from the Digital Signal
Processor (DSP) 130. The selection switch 120 also selects the
appropriate filter interfaced to the probe 105, such that a low
pass filter is used during DC measurements and/or an intermediate
or high pass filter is used during the AC impedance measurements.
The selection switch 120 passes the current to an amplifier array
140 which may be comprised of multiple amplifiers or switch the
signals from different electrodes through the same amplifiers when
multiple electrodes are employed. In a preferred embodiment digital
or analogue lock-in amplifiers are used to detect minute signals
buried in noise. This enables the measurement of the signal of
interest as an amplitude modulation on a reference frequency. The
switching element may average, sample, or select the signal of
interest depending on the context of the measurement. This
processing of the signal will be controlled by the DSP following
commands from the CPU. The signals then pass to a multiplexer 150,
and are serialized before conversion from an analogue to a digital
signal by the ADC. A programmable gain amplifier 160 matches the
input signal to the range of the ADC 170. The output of the ADC 170
passes to the DSP 130. The DSP 130 processes the information to
calculate the DC potential and its pattern on the ductal-epithelial
or skin surface as well as over the region of suspicion. In
addition the impedance at varying depth and response of the DC
potential and impedance to different ECM concentrations of ions,
drug, hormones, or other agent are used to estimate the probability
of cancer. The results are then sent to the CPU 180 to give a test
result 185.
[0153] Alternatively the signal interpretation may partly or
completely take place in the CPU 180. An arbitrary waveform
generator 190 or sine wave frequency generator will be used to send
a composite waveform signal to the probe electrodes and tissue
under test. The measured signal response (in the case of the
composite wave form stimulus) may be deconvolved using FFT (Fast
Fourier Transforms) in the DSP 130 or CPU 180 from which the
impedance profile is measured under the different test conditions.
An internal calibration reference 195 is used for internal
calibration of the system for impedance measurements. DC
calibration may be performed externally, calibrating the probe
being utilized against an external reference electrolyte
solution.
[0154] FIG. 2 includes a handheld probe 400, consistent with the
present invention, which may be applied to the surface of the
breast. The probe may include a handle 410. The probe 400 may be
attached, either directly or indirectly using, for example,
wireless technology, to a measurement device 420. The probe 400 may
be referenced to an intravenous electrode, a skin surface
electrode, other ground, nipple electrode, or ductal probe
electrode within the duct or at the nipple orifice. In one
embodiment, illustrated in FIG. 2, the reference is a nipple
electrode or ductal probe 430, illustrated in greater detail at
close-up 440. One advantage of this configuration is that DC
electropotential and impedance can be measured between the nipple
electrode 430 and the probe 400. The measurement is thus a
combination of the DC potentials or/and impedance of the breast
ductal epithelium, non-ductal breast-parenchyma, and the skin.
[0155] Referring to close-up 440, the ductal probe is inserted into
one of several ductal orifices that open onto the surface of the
nipple. Ductal probe 443 is shown within a ductal sinus 444, which
drains a larger collecting duct 445.
[0156] Another advantage of using a nipple electrode is that a
solution for irrigating the ductal system may be exchanged through
the probe, permitting introduction of pharmacological and/or
hormonal agents. As shown in magnified nipple probe 443, 443' fluid
can be exchanged through a side port. Fluid may be infused into the
duct and aspirated at the proximal end (away from the nipple) of
the nipple probe. Different electrolyte solutions may be infused
into the duct to measure altered permeability of the ductal
epithelium to specific ions or the epithelium may be probed with
different drugs to identify regions of abnormality. Estradiol, or
other hormonal agents, may be infused into a breast duct to measure
the abnormal electrical response associated with pre-malignant or
malignant changes in the epithelium.
[0157] It should be understood that different configurations may
also be used, such as a modified Sartorius cup that applies suction
to the nipple. With this configuration, gentle suction is applied
to a cup placed over the nipple. Small amounts of fluid within the
large ducts and duct sinuses make contact with the electrolyte
solution within the Sartorius cup, establishing electrical contact
with the fluid filling the breast ducts. DC or AC measurements may
then be made between the cup and a surface breast probe.
[0158] FIG. 3 illustrates the probe 400 of FIG. 2 in greater
detail. The skin contact of the surface 450 is placed in contact
with the breast. The surface electrodes 451 measure DC or AC
voltages. The current passing electrodes 452 are used for impedance
measurements. Probe 400 may also include one or more recessed wells
containing one or more ECMs. Multiple sensor electrode arrays may
be attached to the surface probe together with current passing
electrodes. The individual electrodes may be recessed and ECMs with
different composition may be used to pharmacologically,
electrophysiologically, or hormonally probe the deeper tissues or
epithelium under test. Spacing of the electrodes may be greater for
the breast configuration than for other organ systems so that
deeper tissue may be electrically probed and the impedance of the
deeper tissue evaluated. This probe may either be placed passively
in contact with the surface of the breast or held in place by
pneumatic suction over the region of interest. Ports may be placed
for the exchange of solutions or for fluid exchange and suction
(not shown). Guard rings (not shown) may be incorporated to prevent
cross-talk between electrodes and to force current from the contact
surface into the breast. In this configuration there are four
current passing electrodes [453] each positioned radially
90.degree. apart. This permits current to be passed and the voltage
response to be measured in perpendicular fields. The electrodes
will be interfaced via electrical wire, or wireless technology,
with the device described in FIG. 1 above.
[0159] Further embodiments of this technique may involve the use of
spaced electrodes to probe different depths of the breast, and the
use of hormones, drugs, and other agents to differentially alter
the impedance and transepithelial potential from benign and
malignant breast tissue, measured at the skin surface. This enables
further improvements in diagnostic accuracy.
[0160] FIG. 4 illustrates a nipple cup electrode [500] that may be
used as a reference, current passing, voltage measuring or
combination electrode [502]. In this configuration suction and
fluid exchange is applied to the electrode housing [501] through a
side port [510] connected by a flexible hose [515] to a suction
device, aspirator or syringe (not shown). The flange [503] at the
base of the cup is applied to the areola of the breast [520].
Pneumatic suction is applied through the side port and communicated
to the housing by passage [512] so as to obtain a seal between the
breast [520] and the nipple electrode [501]. Electrolyte solution
is used to fill the cup and make electrical contact with the
underlying ductal system. Fluid may be exchanged, or
pharmacological and hormonal agents introduced, by applying
alternating suction and injecting fluid or drugs into the cup
through the side port. The pneumatic suction will open up the duct
openings [505] either by itself or after preparation with alcohol
or de-keratinizing agents to remove keratin plugs at the duct
openings at the surface of the nipple. The nipple cup electrode
[502] may be interfaced by means of an electrical connection [530]
or by a wireless connection (not shown) with the devices
illustrated in FIGS. 1-3 to obtain DC potential, AC impedance or
combination measurements.
[0161] FIG. 5 illustrates an alternative approach where an
individual duct is probed with a flexible catheter electrode [550]
attached to a syringe [555]. This may be used when a specific duct
produces fluid and diagnosis is to be performed on the specific
ductal system producing the fluid. In this configuration a saline
filled syringe is connected to a flexible electrode [550], which is
inserted into the duct [551]. Fluid may be exchanged, or drugs and
hormones may be infused into the duct, through the catheter. An
electrode within, or attached to the syringe makes electrical
contact with the individual ductal system, and the surface probe
electrodes [552] complete the circuit so that the DC potential, AC
impedance or a combination of both may be measured across the
ductal epithelium, skin and intervening breast parenchyma in
combination with the systems described in FIGS. 1-3. Another
approach would be to use a ductoscope in combination with a surface
probe with the electrode(s) interfaced with the ductoscope.
[0162] Devices to measure the electrophysiological characteristics
of tissue and the differences between normal and abnormal tissue
may include those known in the art such as electrical meters,
digital signal processors, volt meters, oscillators, signal
processors, potentiometers, or any other device used to measure
voltage, conductance, resistance or impedance.
[0163] DC potential is usually measured using a voltmeter,
consisting of a galvanometer in series with a high resistance, and
two electrodes (one working and one reference). Voltmeters may be
analog or digital. Ideally these should have an extremely high
input resistance to avoid current-draw. DC potential may also be
measured with an oscilloscope.
[0164] Impedance may be measured using a number of approaches.
Without limitation, examples include phase-lock amplifiers, which
may be either digital or analog lock-in amplifiers. Pre-amplifiers
may be used in conjunction with the lock-in amplifier to minimize
stray currents to ground improving accuracy. Digital lock-in
amplifiers are based on the multiplication of two sine waves, one
being the signal carrying the amplitude-modulated information of
interest, and the other being a reference signal with a specific
frequency and phase. A signal generator can be used to produce the
sine waves or composite signal to stimulate the tissue. Analog
lock-in amplifiers contain a synchronous rectifier that includes a
phase-sensitive detector (PSD) and a low-pass filter. Other
approaches include the use of an impedance bridge with an
oscillator to produce an AC sine wave. These devices when automated
are referred to as LCR-meters and use an auto-balancing bridge
technique. Constant current or constant voltage current sources may
be used. In one preferred embodiment, a constant current source is
used. Rather than an oscillator with a fixed frequency signal a
signal generator, which produces, superimposed sine waves may be
used.
[0165] The tissue response is deconvolved using fast Fourier
transforms or other techniques. Bipolar, tripolar or tetrapolar
current and voltage electrodes may be used to make measurements. In
one preferred embodiment tetrapolar electrode configurations are
employed to avoid inaccuracies that are introduced due to electrode
polarization and electrode-tissue impedance errors. Rather than
impedance, current density may be measured using an array of
electrodes at the epithelial or skin surface. Impedance may also be
measured using electromagnetic induction without the need for
electrode contact with the skin or epithelium.
[0166] In order to process large amounts of data, the methods of
the present invention could be implemented by software on computer
readable medium and executed by computerized equipment or central
processor units.
Example 1
Breast Cancer
[0167] As mentioned above, impedance and DC electrical potential
have been used separately at the skin's surface to diagnose breast
cancer. Neither of these methods measures the ductal
transepithelial DC or AC electrical properties of the breast. This
significantly reduces the accuracy of the approach, because the
origins of breast cancer are within the ductal epithelium, and not
the surrounding breast stroma. Accuracy is further improved when
the transepithelial measurements of impedance and DC potential are
combined. The use of pharmacological and/or hormonal agents in
combination with impedance or DC electrical potential measurements,
provide a more effective method for detecting abnormal
pre-cancerous or cancerous breast tissue.
[0168] Breast cancer develops within a background of disordered
proliferation, which primarily affects the terminal ductal lobular
units (TDLUs). The TDLUs are lined by epithelial cells, which
maintain a TEP (transepithelial potential). In regions of
up-regulated proliferation, the ducts are depolarized. The
depolarization of ducts under the skin surface results in skin
depolarization. The depolarization is significantly attenuated
compared to that which is observed using a transepithelial ductal
approach, as opposed to a non-transepithelial skin surface approach
such as disclosed in U.S. Pat. Nos. 6,351,666; 5,678,547;
4,955,383. When a tumor develops in a region of up-regulated
proliferation, the overlying breast skin becomes further
depolarized compared with other regions of the breast and the
impedance of the cancerous breast tissue decreases. The changes in
ductal epithelial impedance are not measured using existing
technologies resulting in a diminution in accuracy. Alterations in
TEP and impedance occur under the influence of hormones and
menstrual cycle.
[0169] For example, the electrophysiological response of breast
tissue to 17-.beta.-estradiol has been observed to be different in
pre-cancerous or cancerous epithelium than in normal breast
epithelium. In one method of the present invention, estradiol is
introduced directly into the duct or systemically following
sublingual administration of 17-.beta.-estradiol (4 mg). This agent
produces a rapid response, which peaks at approximately 20 minutes.
The electrophysiological response depends, in part, on the stage of
the patient's menstrual cycle, as well as the condition of the
breast tissue. Specifically, in normal breast tissue, a rise in TEP
will occur during the follicular (or early) phase. In pre-cancerous
or cancerous tissue, this response is abrogated. Post-menopausal
women at risk for breast cancer may have an exaggerated TEP
response to estradiol because of up-regulated estrogen receptors on
epithelial cell surfaces.
[0170] Furthermore, estrogen, progesterone, prolactin,
corticosteroids, tamoxifen or metabolites, (all of which alter the
ion transport characteristics of ductal epithelium depending on its
premalignant, malignant and functional state), thereof may be
introduced either orally, intravenously, transcutaneously, or by
intraductal installation.
[0171] In one embodiment of the present invention, breast or other
cancers may be diagnosed by examining the basal conductance state
of the paracellular pathway of the epithelium. For example, in the
breast, a substance known to affect the conductance of the tight
junctions may be infused into the duct, or administered by other
mean, and the transepithelial impedance and/or the DC potential of
the breast is measured, before and after the administration of the
agent, using a combination of surface, nipple, ductal or other
electrodes. The difference in the transepithelial electrical
response of the tight junctions to the agent in normal compared to
pre-malignant or malignant breast epithelium is then is used to
diagnose the presence or absence of malignancy.
[0172] In another embodiment, the electrodes are placed over the
suspicious region and the passive DC potential is measured. Then AC
impedance measurements are made as discussed below. The variable
impedance properties of the overlying skin may attenuate or
increase the measured DC surface electropotentials. Alternatively,
impedance measurements at different frequencies may initially
include a superimposed continuous sine wave on top of an applied DC
voltage. Phase, DC voltage and AC voltage will be measured. The
resistance of the skin or other epithelium at AC and a different
resistance at DC are measured. Under DC conditions since there is
no phase shift, it is possible to measure the transepithelial
potential at the surface. The capacitive properties of the skin may
allow the underlying breast epithelial and tumor potential to be
measured at the skin surface.
[0173] Once the ECM results in "wetting" of the skin surface there
is pseudo-exponential decay in the skin surface potential using the
above referenced approach. Ions in the ECM diffuse through the skin
and make it more conductive, particularly because of changes in the
skin parallel resistance. The time constant for this decay is
inversely proportional to the concentration and ionic strength of
the gel. Once the skin is rendered more conductive by the ECM the
capacitive coupling of the surface to the underlying potential of
the tumor or the surrounding epithelium is lost so that the
measured potential now reflects an offset and diffusion potential
at the electrode-ECM-skin interfaces.
[0174] FIG. 6 demonstrates the effect of varying the ionic content
of the bathing Ringers solution on transepithelial conductance. The
human breast epithelial cells were grown as monolayers on Millipore
filters and grew to confluence in 7 to 10 days. The epithelia were
then mounted in modified Ussing chambers and the DC conductances
were measured using a voltage clamp. The conductance was measured
by passing a 2 .mu.A current pulse for 200 milliseconds and
measuring the DC voltage response and calculating the
transepithelial conductance (y-axis), and plotting it against time
(x-axis). The conductance was measured first in standard Ringer
solution, then in a sodium-free Ringer, then returned to standard
Ringer, then in a potassium-free Ringer and finally returning to
standard Ringer solution while maintaining normal osmolality during
the studies.
[0175] The upper plot (filled squares and solid line) demonstrates
the conductance of benign human breast epithelia grown as a
monolayer. The conductance is higher in the benign epithelial
cells. The Na.sup.+ and K.sup.+ components of conductance are
approximately, 10 and 5 mScm.sup.2 respectively.
[0176] The lower plot (filled circles and dotted line) demonstrates
the conductance of malignant human breast epithelia grown as a
monolayer. The conductance is significantly lower in the malignant
epithelial cells. The Na.sup.+ and K.sup.+ components of
conductance are approximately, 4 and 1 mScm.sup.-2
respectively.
[0177] In malignant tumors as opposed to monolayers of malignant
epithelial cells, the tight junction between cells break down and
the tumor becomes more conductive than either benign or malignant
epithelial monolayers. This observation may be exploited in the
diagnosis of breast cancer. The lower conductance of the epithelium
around a developing tumor, together with a region of high
conductance at the site of the malignancy, may be used to more
accurately diagnose breast cancer. Using electrodes with ECMs with
different ionic composition will permit the specific ionic
conductances to be used in cancer diagnosis. For example a high
conductance region with a surrounding area of low K-conductance is
indicative of breast cancer; a high conductance area with a
surrounding region of normal conductance may be more indicative of
fibrocystic disease (a benign process).
[0178] FIG. 7 demonstrates measurements of cell membrane potential
(.psi.) in human breast epithelial cells. Measurements were made
using a potentiometric fluorescent probe, and ratiometric
measurements, which are calibrated using valinomycin and
[K.sup.+]-gradients. .psi.s were measured in the presence (closed
circles) and absence (open circles) of estradiol (the active
metabolite of estrogen). Each symbol is the mean measurement. The
upper error bar is the standard error of the mean, and the lower
error bar is the 95% confidence level for the observations. The
addition of estrogen to cultured breast epithelial cells results in
an instantaneous increase in .psi. (data not shown) as well as the
transepithelial potential see FIG. 8. Transepithelial potential
(V.sub.T) of an epithelium is the sum of the apical (luminal) cell
membrane potential (V.sub.A) and the basolateral (abluminal) cell
membrane potential (V.sub.BL). Therefore V.sub.T=V.sub.A+V.sub.BL
(changes in V.sub.A and/or V.sub.BL will therefore alter V.sub.T or
transepithelial potential).
[0179] FIG. 7 demonstrates that benign breast epithelial cells have
a .psi. of approximately -50 mV in the absence of estradiol and -70
mV when estradiol is added to the culture media. Malignant and
transformed cells have a .psi. of between -31 and -35 mV in the
absence of estradiol and approximately 50 mV when estradiol is
present in the culture medium.
[0180] The difference in the electrical properties may be exploited
to diagnose breast cancer in vivo. Surface electropotential
measurements are a combination of the transepithelial potential,
tumor potential and overlying skin potential. Physiological doses
of estradiol may be administered to the patient to increase .psi.
and the sustained effect of estradiol results in an increase in
transepithelial potential and tumor potential measured as an
increase in surface electropotential. The increase following
sustained exposure (as opposed to the instantaneous response) is
less in malignant than benign breast tissue.
[0181] It should be noted that the instantaneous response,
illustrated in FIG. 8, is greater in malignant epithelia, whereas
the chronic or sustained exposure to estradiol results in a lower
increase in TEP (transepithelial electropotential) in malignant
cells. Concurrent measurement of surface electropotential and
impedance allow the more accurate diagnosis of cancer. FIG. 8
demonstrates the instantaneous effect of increasing doses of
estradiol on the transepithelial potential (TEP) of benign and
malignant human breast epithelial cells. The cells were grown as
monolayers on Millipore filters and grew to confluence in 7 to 10
days. The epithelia were then mounted in modified Ussing chambers
and the TEP was measured using a voltage clamp. Increasing doses of
estradiol between 0 and 0.8 .mu.M were added (x-axis). The
transepithelial potential was measured after each addition and the
TEP was measured (y-axis).
[0182] The different dose response is apparent for benign and
malignant epithelia. Malignant epithelia have a lower TEP but
undergo an instantaneous increase in TEP of approximately 9 mV
(becomes more electronegative and reaches a level of <-6 mV)
after exposure to only 0.1 .mu.M estradiol and then depolarize to
approximately -2 mV with increasing doses of estradiol up to about
0.5 .mu.M. Benign epithelia have a lesser response to increasing
doses of estradiol and do not peak until almost 0.3 .mu.M and then
remain persistently elevated (higher electro negativity), unlike
the malignant epithelia, with increasing doses of estradiol.
[0183] This difference in dose response may be exploited to
diagnose breast cancer. Estradiol, or other estrogens, at a low
dose will be administered systemically, transcutaneously,
intraductally, or by other route. The instantaneous response of the
surface electropotential and/or impedance may then be used to
diagnose breast cancer with improved accuracy over existing
diagnostic modalities using impedance or DC measurement alone.
[0184] FIG. 9 shows conductance measurements made at 2000 Hz at the
surface of the breast. At this frequency the influence of the
overlying skin impedance is less. There is still however some
variable component of skin impedance, which results in significant
variability of the measurement as evidenced by the overlapping
error bars. Each symbol represents the median measurement with
error bars the standard deviation of the mean.
[0185] Open symbols represent measurements made in patients with a
biopsy proven malignancy, while closed symbols represent
measurements made in patients whose subsequent biopsy proved to be
a benign process such as fibrocystic disease. Malignant lesions are
often associated with surrounding breast epithelium that
demonstrates Up-regulated proliferation. These regions ("adjacent
region") are depolarized and may have a lower conductance than
either over the region of malignancy. This decreased conductance
may be because of decreased K.sup.+-conductance of the adjacent and
pre-malignant epithelium as I have observed in human colon.
[0186] Each of the three groups of symbols represents measurements
from over a suspicious lesion or region, then the adjacent region,
and then over normal breast in an uninvolved quadrant of the
breast. The first two symbols (circles) in each of the three groups
are impedance measurements where the median value is plotted
against the left y-axis as conductance in mScm.sup.-2. The second
two symbols (squares) is the surface electrical potential measured
in mV and plotted against the right y-axis; each division equals 5
mV. The third two symbols (triangles) are the electrical index for
benign and malignant lesions and are in arbitrary units and are
derived from the conductance and surface potential measurement. It
is immediately apparent that there is less overlap in the error
bars (standard deviation of the mean). Therefore breast cancer can
be more accurately diagnosed using a combination of surface
potential measurement and AC-impedance measurements. Further
enhancements of this technique will involve the use of spaced
electrodes to probe different depths of the breast, and the use of
the hormones, drugs and other agents to differentially alter the
impedance and transepithelial potential from benign and malignant
breast tissue, and measured at the skin or duct surface. This will
enable further improvements in diagnostic accuracy.
[0187] It should be understood that the surface potential
measurement of breast tissue varies based on the position of the
woman in her menstrual cycle. FIG. 10 illustrates this variance.
This figure demonstrates electropotential measurements taken over
the surface of each breast at 8 different locations with an array
of 8 electrodes on each breast referenced to an electrode on the
skin of the upper abdomen. Measurements are taken with error bars
equal to the standard error of the mean. Filled circles and filled
squares represent the median value from the left and right breast
respectively. The vertical dotted line is the first day of each
menstrual cycle.
[0188] It can be seen that the median values for each breast tend
to track one another with lower values in the first half of
menstrual cycle (follicular phase) and higher values in the latter
part of cycle (luteal phase). Although the measured electrical
values are not completely superimposed, because of other factors
affecting the electropotential of the breast, it can be seen that
the lowest levels of electropotential are observed 8-10 days before
menstruation and the rise to the highest levels around the time of
menstruation. This may be because estradiol levels are higher in
the second part of menstrual cycle and directly affect breast
surface electropotential.
[0189] The cyclical pattern of electropotential activity when a
breast cancer or proliferative lesion is present is quite
different. Similarly higher levels of surface electropotential are
observed when measurements were made in the afternoon compared with
the morning. This information can be exploited in a number of
different ways. Measurement of the surface potential and impedance
at different times during cycle enables a more accurate diagnosis
because of a different cyclical change in surface electropotential
(i.e., the peak to peak change in potential is less over a
malignant region, relative to normal areas of the breast).
Secondly, estradiol or another agent that changes the
electropotential of the breast may be administered systemically,
topically (transdermal), intraductally or by other means, and the
drug or hormone-induced change in surface potential may be used as
a provocative test to diagnose breast cancer.
[0190] FIG. 11 is a diagram illustrating the histological and
electrophysiological changes that occur during the development of
breast cancer. The continuum from normal ductal epithelium, through
hyperplasia, atypical hyperplasia, ductal carcinoma in situ (DCIS),
to invasive breast cancer is thought to take 10 to 15 years. Some
of the steps may be skipped although usually a breast cancer
develops within a background of disordered ductal proliferation.
The normal duct maintains a transepithelial potential (inside of
duct negatively charged), which depolarizes and impedance, which
increases during the development of cancer. Once an invasive breast
cancer develops the impedance decreases with loss of tight junction
integrity, and conductance through the tumor is enhanced. The
disordered ducts have altered electrophysiogical and ion transport
properties. These properties are illustrated in the lower aspect of
FIG. 11. These electrophysiological and transport alterations will
be exploited to diagnose cancer and premalignant changes in the
breast.
[0191] In these ways breast cancer can be more accurately diagnosed
using transepithelial measurements of potential, or impedance, or a
combination of transepithelial surface potential measurement,
AC-impedance measurements and pharmacological manipulations.
Example 2
Chemopreventative and Therapeutic Use
[0192] In addition to the ionic, pharmacologic, and hormonal agents
described above, the system and method of the present invention may
be used with cancer preventative and therapeutic agents and
treatments. Specifically, electrical measurement of altered
structure and function provides a method for evaluating a patient's
response to the drugs without requiring a biopsy and without
waiting for the cancer to further develop. Patients who respond to
a given chemopreventative or therapeutic agent would likely show
restoration of epithelial function to a more normal state. Patients
who do not respond would show minimal change or may even
demonstrate progression to a more advanced stage of the disease.
This system and method, thus, may be used by either clinicians or
drug companies in assessing drug response or by clinicians in
monitoring the progress of a patient's disease and treatment, or
monitoring the process of carcinogenesis (cancer development),
before an overt malignancy has fully developed.
Example 3
Electrophysiological Changes in Other Epithelia
[0193] The examples illustrated by FIGS. 12 and 13 were performed
in human colon specimen removed at the time of surgery. Based on in
vitro studies in breast epithelial tissues, similar changes in
human ductal epithelium that can be measured in vivo are
expected.
[0194] FIG. 12 demonstrates the short circuit current (I.sub.SC) of
human colonic epithelium ex-vivo. The figure demonstrates the time
course along the x-axis while varying the potassium gradient across
the tissue. The potassium permeability of the apical membrane of
human colonic mucosa (P.sup.K.sub.a) was determined in surgical
specimens of controls and grossly normal-appearing mucosa obtained
10-30 cm proximal to colorectal adenocarcinomas. The mucosa was
mounted in Ussing chambers and the basolateral membrane resistance
and voltage were nullified by elevating the K.sup.+ in the serosal
bathing solution. The apical sodium (Na.sup.+) conductance was
blocked with 0.1 mM amiloride. This protocol reduces the equivalent
circuit model of the epithelium to an apical membrane conductance
and electromotive force in parallel with the paracellular pathway
as has been verified by microelectrode studies. Increasing serosal
K.sup.+ caused the I.sub.sc to become negative (-140 .mu.A/cm2) in
normal colon after which 30 mM mucosal TEA caused an abrupt
increase in I.sub.sc corresponding to block of apical K.sup.+
channels. In cancer-bearing colon the reduction in I.sub.sc is to
-65 .mu.A/cm.sup.2. The serosal bath was remained constant at 125
mM [K].
[0195] FIG. 13 demonstrates that .DELTA.Isc, determined with
respect to the I.sub.sc at 125 mM mucosal K, is a linear function
of the concentration gradient, .DELTA.[K]. Because the voltage
across the apical membrane is zero under these conditions and the
paracellular pathway is nonselective, the P.sup.K.sub.a (apical
potassium permeability) can be calculated using the Fick equation
i.e., I.sub.sc=FP.sup.K.sub.a.DELTA.[K] where F is the Faraday
constant and .DELTA.[K] is the concentration difference for K.sup.+
across the epithelium. FIG. 13 demonstrates mean.+-.sem values for
I.sub.sc in both normal and premalignant human distal colon. The
apical K.sup.+ permeability of controls was 9.34.times.10.sup.-6
cm/sec and this was significantly reduced by 50% in premalignant
human mucosa to 4.45.times.10.sup.-6 cm/sec. P.sup.K.sub.a could
also be calculated for the change in I.sub.sc when the K.sup.+
channels were blocked with TEA, assuming complete block. This
resulted in somewhat lower values of 6.4.times.10.sup.-6 cm/sec and
3.8.times.10.sup.-6 cm/sec corresponding to a 40% reduction in
P.sup.K.sub.a.
[0196] These observations show that there is a field change in the
K.sup.+ permeability and conductance of human colon, during the
development of cancer. Similar results are expected in breast
ductal epithelium. Impedance measurements, and/or DC measurement
using electrodes with different potassium gradients together with
specific drugs, such as amiloride to block the contributions of
electrogenic Na.sup.+ transport; to the electrical properties of
the breast may be useful to diagnose breast cancer. Amiloride may
be introduced through the breast duct and then the
K.sup.+-concentration varied in the ECM used in the nipple
electrode or irrigated into the duct to measure the reduced
potassium permeability observed in the surrounding breast ductal
epithelium (with atypical ductal hyperplasia or early DCIS), or
increased permeability in the region of the developing invasive
breast cancer.
[0197] FIG. 14 illustrates multiple Nyquist impedance plots from
human breasts. Current was passed between a nipple cup electrode
containing a physiological saline solution under suction to open up
the breast ducts on the surface of the nipple, and an electrode
placed on the surface of the breast. Voltage was then measured
between the nipple and the region of interest using a separate set
of voltage measuring electrodes. All measurements were made at 59
frequencies logarithmically spaced between 60,000 hertz and 1 hertz
except for the fibrocystic with atypia case (filled squares), which
was measured at 59 frequencies between 60,000 hertz and 0.1 hertz.
The impedance curves demonstrate the lowest impedance at highest
frequencies. As the frequency of the applied sine wave decreases
the curves shift from left to right along the x-axis.
[0198] FIG. 15 illustrates the impedance profile for a patient with
a hemorrhagic cyst. These studies were performed at frequencies
from 60,000 hertz to 0.1 hertz. Measurements were made over the
mass (lesion) in the 4 o'clock location of the breast and control
measurements were made in the 10 o'clock location of the same
breast. The high frequency measurement demonstrates that the curves
were superimposable. Separation begins at a frequency below 5 Hz.
The resistance of the mass was higher than the control quadrant of
the breast at low frequencies. Surface open circuit potential
measurements showed depolarization of only 2 mV over the mass and
therefore enabled discrimination from cancer despite the high
impedance.
[0199] FIG. 16 illustrates a Bode plot of impedance plots comparing
a patient with fibrocystic disease (0465) and a patient with breast
cancer ((0099). It can be seen that the impedance [Z] and theta
(phase angle) separate at the lowest frequencies (open and closed
symbols). The data for the suspicious mass, which was identified as
fibrocystic disease on pathology, the control region and the
control region from the breast cancer are almost superimposable. At
the low frequency end of the spectrum the cancer (0099D-filled
circles) separates from the control quadrant measurement
(0099C-open circles) at approximately 20 Hz.
[0200] FIG. 17 illustrates the same data as in FIG. 16 plotted as a
Nyquist plot. The mass (a region of fibrocystic disease 0465A-open
squares) has a 5000.OMEGA. lower impedance at the low frequency end
of the curve to the right side of the x-axis, compared with the
control region (0465B filled squares). Plot 0099C (open circles)
has a similar total impedance to the breast with fibrocystic
changes but the curve shows a "double hump" indicating two
different time constants (.tau.) for the low and high frequency
ends of the impedance spectra in the malignant breast. This
characteristic appearance can also be utilized as a diagnostic
tool.
[0201] FIG. 18 demonstrates the impedance spectra when the curve
(0099D-filled circles) is added for the breast cancer to FIG. 17.
The total impedance is significantly higher at 76397.OMEGA.
compared to 45447.OMEGA. for the control quadrant, and the lower
(high frequency) curves begin to separate below about 200 Hz. The
cancer was depolarized by 26 mV compared with the control quadrant,
and the fibrocystic disease was depolarized by 5.5 mV. The
combination of higher impedance and greater depolarization enabled
diagnosis of breast cancer in one patient and fibrocystic disease
in the other despite the fibrocystic patient having impedances
close to 50,000.OMEGA., a high value typically, but not necessarily
suggesting the presence of cancer.
[0202] FIG. 19 illustrates the effects of altering the level of
suction applied to the nipple cup electrode. Holding suction was
established where 3 ml of saline was aspirated from the nipple cup
and is illustrated as the impedance curve with open squares. The
impedance is approximately 26,000.OMEGA.. When an additional 2-3 ml
of saline is aspirated from the nipple cup electrode the impedance
curve collapses to an impedance of approximately 3000.OMEGA.-filled
squares. The addition of 1-2 ml of saline resulted in an increase
in impedance (open circles), which increased to approximately
15000.OMEGA. after 5 minutes (closed circles).
[0203] FIG. 20 illustrates similar suction pressure experiments on
a malignant breast: aspirating 3 ml of physiological saline from
the nipple electrode, after holding suction is obtained, results in
a decrease in total impedance from 45,447.OMEGA. to 29,029.OMEGA.
in the control quadrant whereas impedance decreases from
76,937.OMEGA. to 62,568.OMEGA. over the cancer. The greatest
decrease in impedance is seen at the high frequency end of the
impedance spectra (curves on the left side of the X-axis). For
example, the impedance decreases from 29216 to 1550.OMEGA. in the
control quadrant, and from 35824 to 10106.OMEGA. over the cancer.
On the other hand, the changes in impedance are much less in the
lower frequency spectra (curves on the right-side of the X-axis). A
higher suction results in a decrease in impedance from 19985 to
16593.OMEGA. in the control quadrant whereas the change is even
less over the cancer decreasing from 72674 to 71229.OMEGA..
Capacitance increases in the control quadrant, in the low frequency
range when suction is increased from 1.50E-5 to 1.76E-5 F (farads),
decreased from 1.17E-5 to 9.32E-6 F over the cancer. It can be seen
that altering the suction on the nipple cup electrode manually or
with an automated suction pump can be used to distinguish malignant
from benign breast epithelium by observing different responses of
the impedance spectra to this maneuver.
[0204] FIG. 21 illustrates the method used for estimating the
impedance for the cancer high suction curve in FIG. 20, where an
arc is fitted to the impedance data and extrapolated to the x-axis
at each end of the curve. The difference between the low and high
intercepts is the estimated resistance of 72674.OMEGA.. The
Capacitance (C) is estimated from the reactance at the maximum
height of the arc, and is 1.1652E-5. The Depression Angle (15.932)
is the angle between the x-axis and a line drawn from the origin of
the x-axis to the center of the plotted arc.
[0205] Devices for Use with the Present Invention
[0206] A number of variations are possible for devices to be used
with the present invention. Further, as noted above, within a
device design, there are a number of aspects that may be varied.
These variations, and others, are described below.
[0207] One embodiment of a probe or other device for use in the
present invention includes a plurality of miniaturized electrodes
in recessed wells. Surface recording and initial electronic
processing, such as filtering, may be performed by disposable
commercially-available silicon chips. Each ECM solution or agent
may be specific to the individual electrode and reservoir on the
chip. Thus, for one measurement, a particular set of electrodes
would be used. For another measurement, for example, at a different
ionic concentration, a different set of electrodes would be used.
While this produces some variations, as the electrodes for one
measurement are not located at the same points as for another, this
system provides generally reliable results.
[0208] An alternative approach is to use fewer electrodes and use a
flow-through or microfluidic system to change solutions and drugs.
Specifically, solutions or agents are changed by passing small
amounts of electrical current to move solution or agent through
channels and out through pores in the surface of the device. In
this embodiment, the electrode remains in contact with the same
region of the surface of the breast, thus eliminating
region-to-region variation in measurement. This approach requires
time for equilibration between different solutions. In detecting
the presence of abnormal pre-cancerous or cancerous breast tissue,
a hand-held probe is provided for obtaining surface measurements at
the skin. The probe may include electrodes for passing current as
well as for measuring. An impedance measurement may be taken
between the nipple cup electrode and the hand-held probe, between a
nipple cup electrode and adhesive skin electrodes, between
electrodes on a miniature ductoscope, between electrodes on a
ductoscope and the skin surface electrodes, or may be taken between
electrodes on the hand-held probe. After taking initial DC
measurements, a wetting/permeabilizing agent may be introduced to
reduce skin impedance. The agent may be introduced using a
microfluidic approach, as described above, to move fluid to the
surface of the electrodes. Alternatively, surface electrodes that
just penetrate the stratum corneum may be used to decrease
impedance.
[0209] Fluids for use with the present inventions could include
various electrolyte solutions such as physiologic saline (e.g.
Ringers) with or without pharmacological agents. One preferable
electrolyte solution to infuse into the ductal system will
represent a physiological Ringer solution. Typically this consists
of NaCl 6 g, KCl 0.075 g, CaCl.sub.2 0.1 g, NaHCO.sub.3 0.1 g, and
smaller concentrations of sodium hyper and hypophosphate at a
physiological pH of 7.4. Other electrolyte solution may be used
were the electrolyte comprises approximately 1% of the volume of
the solute. Hypertonic or hypotonic solutions that are greater or
less than 1% may be used in provocative testing of the epithelium
and/or tumor. The concentration of Na, K and Cl will be adjusted
under different conditions to evaluate the conductance and
permeability of the epithelium. Different pharmacological agents
such as amiloride (to block electrogenic sodium absorption),
Forskolin (or similar drugs to raise cyclic-AMP) and hormones such
as prolactin or estradiol can also be infused with the Ringer
solution to examine the electrophysiological response of the
epithelium and tumor to these agents. Similarly, the calcium
concentration of the infusate will be varied to alter the tight
junction permeability and measure the electrophysiological response
of the epithelium to this manipulation. Dexamethasone may be
infused to decrease the permeability of the tight junctions, and
the electrophysiological response will be measured.
[0210] Although specific examples have been given of drugs and
hormones that may be used in "challenge" testing of the epithelium
and tumor, any agonist or antagonist of specific ionic transport,
or tight-junctional integrity, known to be affected during
carcinogenesis may be used, particularly when it is known to
influence the electrophysiological properties of the epithelium or
tumor.
[0211] Regardless of the configuration of the device, a signal is
used to measure either the ductal transepithelial potential by
itself, or the transepithelial impedance. These two measurements
may then be combined to characterize the electrical properties of
the epithelium associated with a developing abnormality of the
breast, and are then compared with uninvolved areas of the same or
opposite breast. Surface electropotential measurements and
impedance measurements are then made to characterize the
non-transepithelial electrical properties of the breast. These
measurements involve DC potential measurements where the surface
potential is referenced to an electrode that is not in contact
directly, or indirectly through an ECM, with the duct lumen.
Impedance measurements are similarly made between surface
electrodes or a surface electrode and a reference electrode not in
contact directly or indirectly (through an ECM) with the ductal
lumen. These measurements are then compared and combined with the
transepithelial electrical measurements to further characterize the
breast tissue.
[0212] Furthermore an understanding of the electrophysiological
basis of the altered impedance or DC potential permits more
accurate diagnosis. For example impedance or DC potential may
increase or decrease because of several factors. Increased stromal
density of the breast may alter its impedance. This is a
non-specific change, which may not have bearing on the probability
of malignancy. On the other hand, a decrease in the potassium
permeability of the epithelia around a developing malignancy would
increase impedance and would be more likely associated with a
developing cancer than a non-specific impedance change. Additional
information is obtained from my method by probing the tissue to
different depths using spaced voltage-sensing electrodes. The use
of electrophysiological, pharmacological and hormonal manipulations
to alter DC potential and/or DC potential differentially in normal
compared to cancer-prone, pre-malignant or malignant tissue is
another significant difference, which enhances the diagnostic
accuracy of my invention over the above referenced ones.
[0213] Although the use of a nipple cup electrode has been
described in this application for use in breast cancer diagnosis, a
cup electrode may be used in other organs where the epithelium may
be difficult to access endoscopically, or an endoscopic approach is
not desired. An example would be the pancreatic and bile ducts,
which join and open at the ampulla of Vater within the second part
of the duodenum. Bile duct tumors develop from the endothelial
lining of the bile duct, (i.e., cholangiocarcinomas, or the
epithelial lining of the pancreatic duct, i.e., pancreatic
carcinomas). The ampulla may be accessed endoscopically and a cup
electrode applied by suction to the ampulla. Physiological saline
can be infused into the ducts and then a transepithelial potential
and impedance could be measured intraoperatively to identify the
region of tumor in the pancreatic, or bile duct using a second
electrode placed on the peritoneal surface of the pancreas or bile
duct. Alternatively, the peritoneal surface electrode may be
replaced by a skin surface, or intravenous electrode when used in a
minimally or non-invasive manner.
[0214] Drugs may be infused though the cup electrode as a
provocative test and described for breast. Secretin for example,
stimulates bicarbonate secretion by the pancreatic ducts. This
response may be abrogated by changes in the epithelium associated
with pancreatic carcinoma. The distribution of muscarinic
receptors, particularly M1 and M3, may be altered in the epithelium
during pancreatic carcinogenesis. Therefore specific muscarinic
agonists (cholinomimetic choline esters and natural alkaloids) and
antagonists (atropine, Pirenzepine (M1), Darifenacin (M3)) may be
used to elicit a particular electrophysiological response due to
chloride secretion in ductal epithelium associated with pancreatic
cancer. Similar approaches may be used in the intra and
extrahepatic bile ducts to diagnose liver cancer.
[0215] Prostatic cancer may be diagnosed using a urethral cup
electrode applied to the external urethral meatus. Physiological
saline is infused into the urethra. Direct electrical connection is
established with the prostatic ductal and acinar epithelium via
prostatic ducts that open into the prostatic urethra. A surface
electrode may then be placed per rectum onto the surface of the
prostate and electrophysiological measurements may be made in a
transepithelial fashion as described in the breast. Similarly,
provocative tests may be performed with drugs and hormones that
differentially affect the electrophysiological characteristics of
abnormal prostatic epithelium when compared to normal prostatic
tissue.
[0216] Endometrial cancer may be diagnosed with an electrode cup
placed on the uterine cervix. Physiological saline may be infused
through the cervical canal to make electrical contact with the
endometrium. Electrophysiological measurements may be made with a
reference electrode, placed on the skin, intravenously or at a
suitable reference point. Alternatively, this approach may be used
during surgery where the cervical cup electrode is used in
conjunction with a reference electrode used on the peritoneal or
outside surface of the uterus.
[0217] Salivary gland tumors open through small ducts into the oral
cavity. For example in the parotid gland, Stensen's duct opens
inside the mouth opposite the second upper molar tooth. A cup
electrode may be used over the opening of the duct inside the
mouth. Physiological saline is infused into the duct and electrical
contact is thus established with the ductal epithelium of the
salivary gland. A surface electrode is then used over the skin
surface of the gland and electrical measurements are used to
establish the diagnosis of cancer.
[0218] Although specific examples have been given above, this
technique may be used to diagnose any tumor, where endoscopic
access to the epithelium is not possible or desired. The
application of physiological saline via a cup or short catheter may
be used for example in the bowel or other organ system where
electrical contact with the epithelium permits a transepithelial
electrophysiological measurement to be made without resorting to
endoscopic electrode placement. The second electrode is then used
to externally scan the organ for the presence of a tumor or
abnormal epithelium. Since the physiological saline acts as an
electrode in direct contact with the epithelium this approach
simplifies the approach to electrophysiological measurements.
Depolarization and the impedance characteristics of the epithelium
will be more accurate when the surface-scanning electrode is in
close proximity to the underlying abnormal epithelium or tumor.
[0219] The embodiments described herein are described in reference
to humans. However, cancers in non-humans may be also diagnosed
with this approach and the present invention is also intended to
have veterinary applications.
[0220] Any range of numbers recited in the specification
hereinabove or in the paragraphs and claims hereinafter, referring
to various aspects of the invention, such as that representing a
particular set of properties, units of measure, conditions,
physical states or percentages, is intended to literally
incorporate expressly herein by reference or otherwise, any number
falling within such range, including any subset of numbers or
ranges subsumed within any range so recited. Furthermore, the term
"about" when used as a modifier for, or in conjunction with, a
variable, characteristic or condition is intended to convey that
the numbers, ranges, characteristics and conditions disclosed
herein are flexible and that practice of the present invention by
those skilled in the art using temperatures, frequencies, times,
concentrations, amounts, contents, properties such as size, surface
area, etc., that are outside of the range or different from a
single value, will achieve the desired results as described in the
application, namely, detecting electrophysiological changes in
pre-cancerous and cancerous tissue and epithelium, for example,
breast tissue.
[0221] All documents described herein are incorporated by reference
herein, including any patent applications and/or testing
procedures. The principles, preferred embodiments, and modes of
operation of the present invention have been described in the
foregoing specification.
[0222] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the various aspects or embodiments of the
present invention as set forth in the application and the appended
claims.
* * * * *