U.S. patent application number 10/025350 was filed with the patent office on 2003-03-06 for circulating insulin-like growth factor-i and prostate cancer risk.
This patent application is currently assigned to Lady Davis Institute. Invention is credited to Giovannucci, Edward, Pollak, Michael N., Stampfer, Meir J..
Application Number | 20030044860 10/025350 |
Document ID | / |
Family ID | 22108389 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030044860 |
Kind Code |
A1 |
Pollak, Michael N. ; et
al. |
March 6, 2003 |
Circulating insulin-like growth factor-I and prostate cancer
risk
Abstract
Methods of predicting a propensity to developing prostate cancer
are presented. The method consists of measuring the IGF status of
individual. Individuals with high IGF status, as compared with
normal reference range values, are at increased risk for developing
prostate cancer. More particularly, the IGF status may be
determined by measuring IGF-I levels and/or IGFBP-3 levels. High
IGF and low IGFBP levels are indicative of a high IGF status. A
method of determining the prognosis of existing prostate cancers or
of monitoring disease progression involves determining the IGF/PSA
status of an individual. Individuals with a high IGF/PSA status
(both high IGF status and high PSA levels) tend to develop severe
prostate cancer and have a poorer overall prognosis.
Inventors: |
Pollak, Michael N.;
(Montreal, CA) ; Stampfer, Meir J.; (Brookline,
MA) ; Giovannucci, Edward; (Wakefield, MA) |
Correspondence
Address: |
HAYNES AND BOONE, LLP
901 MAIN STREET, SUITE 3100
DALLAS
TX
75202
US
|
Assignee: |
Lady Davis Institute
3755 Cote Ste-Catherine Road
Montreal
CA
HCT 1E2
|
Family ID: |
22108389 |
Appl. No.: |
10/025350 |
Filed: |
December 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10025350 |
Dec 18, 2001 |
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09234651 |
Jan 21, 1999 |
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6410335 |
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60072560 |
Jan 21, 1998 |
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Current U.S.
Class: |
435/7.23 ;
702/19 |
Current CPC
Class: |
G01N 33/74 20130101;
G16H 50/30 20180101; A61K 38/00 20130101; G01N 33/57434
20130101 |
Class at
Publication: |
435/7.23 ;
702/19 |
International
Class: |
G01N 033/574; G06F
019/00 |
Claims
What is claimed is:
1. A method of predicting increased risk of prostate cancer in an
individual, comprising: a) measuring the concentration of
insulin-like growth factor (IGF) in a body fluid from an
individual; wherein an elevated concentration of IGF above a
reference range for IGF indicates an increased risk for prostate
cancer.
2. The method of claim 1, wherein said body fluid is selected from
the group consisting of blood, plasma, serum and seminal fluid.
3. The method of claim 1, wherein said IGF is total IGF, free IGF
or complexed IGF.
4. A method of predicting increased risk of prostate cancer in an
individual, comprising: a) measuring the concentration of
insulin-like growth factor-I (IGF-I) in a specimen from an
individual; b) measuring the concentration of insulin-like growth
factor binding protein-3 (IGFBP-3) in a specimen from said
individual; and c) conducting a multivariate adjustment of the
IGF-I concentration relative to the IGFBP-3 concentration to
provide an adjusted IGF-I level; wherein the adjusted IGF-I level
above a reference range for adjusted IGF-I indicates an increased
risk for prostate cancer.
5. The method of claim 4, wherein said specimen is selected from
the group consisting of blood, plasma, serum and seminal fluid.
6. The method of claim 4, wherein said IGF-I is total IGF-I, free
IGF-I or complexed IGF.
7. The method of claim 4, wherein said IGFBP-3 is total IGFPP-3,
free IGFBP-3 or complexed IGFBP-3.
8. A method of predicting increased risk of prostate cancer in an
individual, comprising: a) measuring an IGF status in a body fluid
from an individual; wherein increases in the IGF status as compared
to normal reference values indicates an increased risk for prostate
cancer.
9. The method of claim 8, wherein the IGF status is measured by
measuring both IGF-I and IGFBP-3, IGF-I alone, or IGFBP-3
alone.
10. The method of claim 8, wherein said body fluid is blood,
plasma, serum or seminal fluid.
11. The method of claim 9, wherein said IGF-I is total IGF-I, free
IGF-I or complexed IGF-I.
12. A method of predicting increased risk of prostate cancer with a
poor prognosis, comprising: a) measuring the concentration of
insulin-like growth factor-I (IGF-I) in a specimen from an
individual; b) measuring the concentration of prostate specific
antigen (PSA) in a specimen from said individual; and c) conducting
a multivariate adjustment of the IGF-I concentration relative to
the PSA concentration to provide an adjusted IGF/PSA value; wherein
an adjusted IGF/PSA value above the reference range for adjusted
IGF/PSA indicates an increased risk for prostate cancer with a poor
prognosis.
13. The method of claim 12, wherein said specimen is selected from
the group consisting of blood, plasma, serum and seminal fluid.
14. The method of claim 12, wherein said IGF-I is total IGF-I, free
IGF-I or complexed IGF-I.
15. A method of predicting increased risk of severe prostate cancer
in an individual, comprising: a) measuring the concentration of
insulin-like growth factor-I (IGF-I) in a specimen from an
individual; b) measuring the concentration of insulin-like growth
factor binding protein-3 (IGFBP-3) in a specimen from said
individual; c) measuring the concentration of prostate specific
antigen (PSA) in a specimen from said individual; and d) conducting
a multivariate adjustment of the IGF-I concentration relative to
the IGFBP-3 concentration and PSA concentration to provide an
adjusted IGF/IGFBP/PSA value; wherein an adjusted IGF/IGFBP/PSA
value above the reference range for adjusted IGF/IGFBP/PSA
indicates an increased risk for severe prostate cancer.
16. The method of claim 15, wherein said specimen is selected from
the group consisting of blood, plasma, serum and seminal fluid.
17. The method of claim 15, wherein said IGF-I is total IGF-I, free
IGF-I or complexed IGF-I.
18. The method of claim 15, wherein said IGFBP-3 is total IGFPP-3,
free IGFBP-3 or complexed IGFBP-3.
19. A method of treating prostate cancer, comprising administering
an IGF-axis component modulating agent to an individual with
prostate cancer.
20. A method of claim 18, wherein said IGF-axis component
modulating agent is selected from the group consisting of
somatostatin, somatostatin analogs, and growth hormone releasing
antagonists.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application, Serial No. 60/072,560 filed Jan. 21, 1998.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for assessing the
risk of developing prostate cancer in an individual. Increased risk
for prostate cancer is correlated with high insulin-like growth
factor status (IGF status). Specifically, the method involves
measurement of IGF-I and/or insulin-like growth factor binding
protein-3 (IGFBP-3) in a specimen. High levels of IGF and/or low
levels of IGFBP correlate with increased risk of developing
prostate cancer.
[0004] In an alternative embodiment, the method involves
determining the IGF/PSA status of an individual wherein the
determination of IGF status is combined with a measurement of
prostate specific antigen (PSA) levels. The IGF/PSA status provides
an improved method of assessing the prognosis of existing prostate
cancer.
[0005] Furthermore, novel treatment modalities are suggested by the
discovery of the link between IGF-axis component levels and
prostate cancer that involve modulating IGF-axis component
levels.
[0006] 2. Description of the Prior Art
[0007] Prostate adenocarcinoma accounts for the majority of
malignancies in males over the age of 65. Yearly screening for
prostate cancer is recommended after the age of 45. There has been
considerable effort toward identifying suitable prostate cancer
markers to assist in predicting, diagnosing and monitoring this
disease.
[0008] Prostate specific antigen (PSA) is recognized as the most
sensitive marker of prostatic adenocarcinoma (M. K. Brawer Cancer
71(suppl):899-905 (1993); J. E. Oesterling J. Urol. 145:907-23
(1991)). PSA is also recognized as a proven screening vehicle (P.
H. Gann, et al. Amer. Med. Assoc. 273:289-94 (1995); W. J.
Catalona, et al. J. Urol. 151:1283-90 (1994)). It has been the most
sensitive front line test for identifying prostate gland-contained,
and hence presumably curable, cancer. PSA has also been useful in
detecting clinically significant tumors, as opposed to latent,
indolent micro-carcinomas. Screening for PSA is even superior to
the common office practice of digital rectal examination (DRE). For
example, Labrie et al. (Clin. Invest. Med. 16:425-39 (1993)) showed
that 97% of cancers detected at annual follow-up by DRE plus PSA
testing were PSA-positive. Thus, only a minimal benefit accrues
from including DRE in the medical evaluation.
[0009] Investigators have searched for other markers or indicators
of prostate cancer, but to date PSA has been the most useful
marker. No one has heretofor studied the association of IGF-axis
components with prostate cancer.
[0010] Insulin-like growth factors (IGF-I and IGF-II) belong to
family of peptides that mediate a broad spectrum of growth
hormone-dependent as well as independent mitogenic and metabolic
actions. Unlike most peptide hormones, IGFs in circulation and
other physiological fluids are associated with a group of high
affinity binding proteins (IGFBPs) that specifically bind and
modulate their bioactivity at the cellular level. Under normal
conditions about 95-98% or the IGF-I in human plasma is bound to
IGFBPs. Six structurally homologous IGFBPs with distinct molecular
size, hormonal control, and tissue expression and functions, have
been identified (J. I. Jones, et al. Endocrinol. Reviews 16:3-34,
(1995)). Most serum IGF-I circulates in a relatively stable ternary
complex consisting of IGFBP-3 and a unique leucine-rich,
acid-labile subunit (ALS). Less than one percent of IGF-I is
estimated to exist in a "free" or unbound form.
[0011] The rate of cell proliferation is positively correlated with
risk of transformation of certain epithelial cell types. S. M.
Cohen and L. B. Ellwein. Science 249:1007 (1990); S. M. Cohen and
L. B. Ellwein. Cancer Research 51:6493 (1991). IGFs have mitogenic
and anti-apoptotic influences on normal and transformed prostate
epithelial cells. A. Y. Hsing, K. Kadomatsu, M. J. Bonharn, D.
Danielpour. Cancer Research 56:5146 (1996); Z. Culig, A. Hobisch,
M. V. Cronauer, C. Radmayr, J. Trapman, A. Hittmair, G. Hartsch, B.
Klocker. Cancer Research 54:5474 (1994); P. Cohen, D. M. Peehl, R.
G. Rosenfeld. Hormone and Metabolic Research 26:81 (1994); M.
Iwamura, P. M. Stuss, J. B. Casamento, A. T. Cockett. Prostate
22:243 (1993); P. Cohen, D. M. Peehl, G. Lamson, R. G. Rosenfeld.
J. Clinical Endocrinology & Metabolism 73:401 (1991); R. Rajah,
D. Valentino, and P. Cohen. J. Biol. Chem. 272:12181 (1997). Most
circulating IGF-I originates in the liver, but IGF bioactivity in
tissues is related not only to levels of circulating IGFs and
IGFBPs, but also to local production of IGFs, IGFBPs, and IGFBP
proteases. J. J. Jones and D. R. Clemmons. Endocrine Reviews 16:3
(1995). Person-to-person variability in levels of circulating IGF-I
and IGFBP-3 (the major circulating IGFBP (J. J. Jones and D. R.
Clemmons. Endocrine Reviews 16:3 (1995) is considerable (A. Juul,
P. Bang, N. T. Hertel, K. Main, P. Dalgaard, K. Jorgensen, J.
Muller, K. Hall, N. E. Skakkebaek. J. Clinical Endocrinology &
Metabolism 78:744 (1994); A. Juul, P. Dalgaard, W. F. Blum, P.
Bang, K. Hall, K. F. Michaelsen, J. Muller, N. E. Skakkeback. J.
Clinical Endocrinology & Metabolism 80:2534 (1995) and
heterogeneity in serum IGF-I level appears to reflect heterogeneity
in tissue IGF bioactivity. Acromegaly and growth hormone deficiency
are examples where there are clear changes in tissues that are
correlated with serum IGF-I level, implying a relationship between
serum IGF-I level and tissue IGF-I bioactivity. Also, factors that
decrease circulating IGF-I level also affect expression of genes in
target organs for IGF-I action in a manner that decreases IGF
bioactivity. For example, antiestrogens lower IGF-I level (M.
Pollak, J. Constantino, C. Polyochronakos, S. Blauer, H. Guyda, C.
Redmond, B. Fisher, R. Margolese. JNCI 82:1693 (1990), but also
increase IGFBP expression (H. Huynh, X. Yang, B. Deroo, M. Pollak.
Cell Growth and Differentiation 7:1501 (1996); H. Huynh, X. Yang,
M. Pollak. J Biol Chem 271:1016 (1996) and decrease IGF-I receptor
expression (H. Huynh, T. Nickerson, M. Pollak. Clinical Cancer
Research 2:2037 (1996) in cells that are targets for IGF-I action.
No one has heretofore shown that markers relating to IGF-axis
components can also be used as a risk marker for prostate
cancer.
SUMMARY OF THE INVENTION
[0012] Abbreviations and Definitions
[0013] AAG--3-alpha-androstanediol glucuronide.
[0014] ALS--Acid Labile Subunit. A protein found in the 150 KDa
ternary complex wherein most of the circulating IGF is found. ALS
is sensitive to inactivation by acid.
[0015] Binary complex--A two part complex of IGFBP and ALS or IGFBP
and IGF.
[0016] Body fluid--Any biological fluid, including but not limited
to the following: serum, plasma, lymph fluid, synovial fluid,
follicular fluid, seminal fluid, amniotic fluid, milk, mammary
fluid, whole blood, urine, spinal fluid, saliva, sputum, tears,
perspiration, mucus tissue culture medium, tissue extracts and
cellular extracts. Preferably, the body fluid is blood, plasma,
serum or seminal fluid.
[0017] DHT--Dihydrotestosterone.
[0018] GH--Growth hormone.
[0019] GHBP--GH binding protein.
[0020] IGF--Insulin-like Growth Factor.
[0021] IGF-axis components--Those components that modulate the
IGF/GH cascades including GH, GHBP, GH receptor, IGF, IGF receptor,
IGF proteases, IGFBP 1 through 6 and other IGFBPs, ALS, IGF
proteases, IGF and GH receptor antagonists, and the like.
[0022] IGF-axis component modulating agent--also: IGF status
modulating agents. Includes any agent whose intended effect is to
influence the GH or IGF cascades. Agents include GH, GHBP, IGF,
IGFBP, ALS, IGFBP complex, GH receptors, IGF receptors, antibodies
or modulators of any of the preceding, receptor antagonists for GH
or IGF, or any drug that acts to modulate the IGF status of an
individual including somatostatin, somatostatin analogues, GH
antagonists, IGF antagonist, IGFBP stimulator, and the like.
[0023] IGFBP--Any IGF binding protein, including IGFBP-1 to 6 and
the heretofore unsequenced IGFBPs. Preferably, the IGFBP is IGFBP-3
in the context of the assay described herein.
[0024] IGFBP-3--The major circulating IGF binding protein.
[0025] IGFBP complex--This term is defined herein to include either
the binary complex of IGFBP and ALS or IGF or the ternary complex
of IGFBP and ALS and IGF.
[0026] IGF status--The IGF status of an individual is reflected in
the levels of IGF-axis components. For example a high IGF status is
reflected by high levels of IGF and stimulators of IGF activity and
low levels of inhibitors of IGF activity such as IGFBP. The IGF
status of an individual is now known to vary--either up or down-in
in certain conditions involving the prostate, including but not
limited to, prostate adenocarcinoma or benign prostatic
hyperplasia.
[0027] IGF/PSA status--A combination of IGF status and PSA levels.
Individuals with high IGF/PSA status are at risk for developing
severe prostate cancer. A high IGF/PSA status is reflected by high
IGF and PSA levels and low IGFBP levels.
[0028] RR--Relative risk.
[0029] Risk Index--A value indicating the risk of a patient for
developing prostate disease or poor prognosis for patients with
prostate disease. The risk index can be generated from data
concerning the IGF-axis component levels in a patient, including
IGF or IGFBP levels and/or the PSA levels of a patient.
[0030] SHBG--Sex hormone binding globulin.
[0031] T--Testosterone.
[0032] Ternary complex--The 150 KDa complex composed of IGF, IGFBP
and ALS.
[0033] Treatment designed to influence IGF status--Includes any
medical treatment whose intended effect is to influence the GH or
IGF cascades. Treatments may include treatments with such agents as
GH, GHBP, IGF, IGFBP, ALS, IGFBP complex, GH receptors, IGF
receptors, antibodies or inhibitors of any of the preceding,
receptor antagonists for GH or IGF, or any drug that acts to
modulate the IGF-axis status of an individual. Individuals include
both human and animals, such as pigs, cattle, sheep, goats, horses,
poultry, cats, dogs, fish, etc.
[0034] The present invention relates to assays for measuring IGF-I
levels and their use for predicting, diagnosing and monitoring
prostate cancer. A strong consistent positive association between
IGF-I and prostate cancer risk has been observed, especially with
adjustment for IGFBP-3. High levels of IGF-I are predictive of
increased risk for prostate cancers, whereas IGFBP has a protective
effect. Additionally, the IGF or IGF/IGFBP assay can be combined
with a test for PSA for improved ability to predict patient
prognosis and monitor treatment. Further, these findings suggest
that it is possible to treat prostate cancers with agents that
modulate the IGF-axis components.
[0035] In the its broadest embodiment, a method of predicting
increased risk of prostate cancer in an individual is provided. The
method involves measuring the "IGF status" or concentration of
IGF-axis components in a body fluid from an individual, wherein
changes in the IGF status or concentration of IGF-axis components
as compared to normal reference values indicates an increased risk
for prostate cancer.
[0036] In one embodiment, the invention is a method of predicting
increased risk of prostate cancer in an individual, comprising
measuring the concentration of insulin-like growth factor (IGF-I)
in a body fluid from an individual, wherein an elevated
concentration of IGF-I above a reference range for IGF-I indicates
an increased risk for prostate cancer.
[0037] In another embodiment, the invention is a method of
predicting increased risk of prostate cancer in an individual. The
method involves measuring the concentration of IGF-I and IGFBP in a
specimen from an individual, wherein increased IGF-I and decreased
IGFBP, as compared to a normal reference range value, indicates an
increased risk for prostate cancer.
[0038] In yet another embodiment, the invention is a method of
measuring the IGF/PSA status of an individual. High IGF and PSA
levels and/or low IGFBP levels are indicative of individuals at
risk for severe prostate cancer or who have prostate cancer with a
poor prognosis.
[0039] A multivariate adjustment of the IGF-I concentration
relative to the IGFBP-3 concentration provides an adjusted IGF-I
level or "IGF status" which can be compared to an adjusted normal
reference range value. An algorithm can be designed, by those with
skill in the art of statistical analyses, which will allow the user
to quickly calculate an adjusted IGF level or "IGF status" for use
in making predictions or monitoring prostate disease. With
additional patient data, generated similarly to the manner
described herein, it will be possible to more accurately define
normal reference range values for IGF status parameters. The
algorithm and normal reference values can be used to generate a
device that will allow the end user to input IGF, IGFBP and quickly
and easily determine the IGF status or risk index of an individual.
Similarly, it is possible to provide a device that indicates the
IGF/PSA status of an individual.
[0040] Finally, the invention pertains to a method of treating
prostate cancer, comprising administering an IGF-axis component
modulating agent to an individual with prostate cancer.
DETAILED DESCRIPTION OF THE INVENTION
[0041] As used herein the term "prostate disease" includes diseases
or disorders associated with pathologic conditions of the prostate,
including, but not limited to prostate cancer or benign prostatic
hyperplasia. The method of the present invention is most preferably
used to determine the risk of an individual developing prostate
cancer, diagnosing prostate cancer or assessing the progress of the
cancer. Accordingly, the method of the present invention may be
useful in predicting prostate cancer, differentiating cancer from
other prostatic diseases.
[0042] A suitable specimen is collected from an individual.
Suitable specimens include any body fluid or tissue known to
contain IGF-axis components and/or PSA. Preferably, the specimen is
blood, serum, plasma or seminal fluid. The specimen may be
collected by venipuncture or capillary puncture, and the specimen
collected into an appropriate container for receiving the specimen.
Alternatively, the specimen may be placed onto filter paper.
[0043] The IGF-axis components and/or PSA can be measured by
techniques well known to those skilled in the art, including, but
not limited to immunoassays such as enzyme-linked immunosorbent
assay (ELISA), enzyme immunoasssay (EIA), fluorescence polarization
immunoassay (FPIA), fluorescence immunoassay (FIA) and
radioimmunoassay (RIA). The assays described in U.S. application
Ser. Nos. 08/626,641, 08/643,830, 08/763,244 and 08/829,094 are
particularly suitable and are incorporated herein by reference.
Further, the concentrations of the IGF-axis components and/or PSA
may, for example, be measured by test kits supplied by DIAGNOSTIC
SYSTEMS LABORATORIES, INC., Webster, Tex., USA.
[0044] In a preferred embodiment, total IGF-I can be measured. In
some cases, it may be advantageous to measure total, bound and/or
free IGF-I. For example, suitable highly specific and simple
non-competitive ELISAs for reliable determination of IGF-I (M. J.
Khosravi, et al., 1996 Clin. Chem. 42:1147-54), IGFBP-3 (Khosravi
J. et al. 1996 Clin. Chem. S6:234) and IGFBP-1 (M. J. Khosravi, et
al. 1996 Clin. Chem. S6:171) have been described. The high affinity
antibodies incorporated in these immunoassays have been selected
for lack of cross-reactivity or interference by the closely related
peptides or binding protein.
[0045] Additionally, IGFBPs can be used as an indicator of
decreased risk for prostate cancer. Preferably, the binding protein
is IGFBP-3 and total, complexed and/or free IGFBP-3 may be
measured. In alternative embodiments, the other IGFBPs (such as,
but not limited to IGFBP-1) may also be used to predict the risk of
prostate cancer. Additionally, acid-labile subunit (ALS) may also
be used to predict susceptibility to prostate cancer. The ALS may
be total ALS, complexed and/or free ALS. Other IGF-axis components
may also influence the risk of prostate cancer.
[0046] Men in the highest quartile of circulating IGF-I have a
relative risk of prostate cancer of 4.32 (95 percent confidence
interval (CI) 1.76-10.6) compared to men in the lowest quartile,
and there was significant linear trend such that a 100 ng/ml
increase in IGF-I level was associated with a doubling of risk
(p=0.001). Furthermore, this association is evident among men with
normal as well as elevated baseline prostate specific antigen (PSA)
levels. These results indicate that circulating IGF-I is predictor
of prostate cancer risk, and perhaps progression, and thus have
implications for risk reduction and treatment strategies.
EXAMPLE 1
[0047] This example shows that a higher serum IGF-I level is
related to higher risk of developing prostate cancer. In view of
the direct and indirect growth inhibitory properties of IGFBP-3
(reviewed in Rechler, M. Endocrinology 138:2645-2647 (1997)), we
also postulated that high levels of IGFBP-3 would be inversely
related to risk.
[0048] We used a nested case-control study within the Physician's
Health Study (The Physicians' Health Study began in 1982 as a
randomized double-blinded placebo-controlled trial of beta-carotene
and aspirin in 22,017 U.S. male physicians age 40-82) (Steering
Committee of the Physicians' Health Study Research Group. N. Eng.
J. Med. 321:129 (1989)). The study excluded men with a history of
myocardial infarction, stroke, transient ischemic attacks, unstable
angina, cancer (except for non-melanoma skin cancer), current renal
or liver disease, peptic ulcer, gout, contraindication to use of
aspirin, or current usage of aspirin, other platelet-active agents,
or vitamin A supplements. Each participant supplied written
informed consent and permission to review medical records, and the
project has been continuously approved by the Institutional Review
Board at Brigham and Women's Hospital in accord with federal
regulations) to examine serum IGF-I, IGF-II, and IGFBP-3 levels in
relation to prostate cancer risk. At baseline, the men aged 40 to
82 provided information via mailed-in questionnaires on personal
history of disease, usage of aspirin, vitamins, smoking habits,
blood pressure, cholesterol levels, height, weight, and diet.
14,916 (68%) of the randomized physicians also provided blood
specimens in 1982 (Before randomization, the men were mailed blood
kits with instructions to have their blood drawn into vacutainer
tubes containing EDTA (anti-coagulant), to centrifuge them and to
return the plasma in polypropylene cryopreservation vials by
overnight pre-paid courier. Cold packs, provided with the kits,
were used to keep specimens cool until receipt the following
morning, when they were aliquotted and stored at -82 degrees C. No
specimen thawed or warmed substantially during storage). Through
1992, over 99% of surviving participants completed annual
questionnaires reporting morbidity events and vital status was
ascertained for 100%.
[0049] Following a report of prostate cancer in the annual
questionnaires, we obtained medical records and pathology reports
which were reviewed by physicians in the End Points Committee.
Stage at diagnosis, tumor grade, Gleason score, type of
presentation (e.g. symptoms and screening rectal examination),
prostate specific antigen (PSA) level immediately before treatment,
and treatment method were determined from medical record review by
physician investigators (The Whitmore-Jewett classification scheme
was used to identify stage, and cases without pathological staging
were considered indeterminate, unless there was evidence of
metastases. "High grade/stage cancer" were those cases presenting
as stage C or D, or stage A, B, or indeterminate with either poor
histological differentiation or a Gleason score of seven or
higher).
[0050] Cases and controls were selected from among the 14,916
physicians who provided blood. As of March 1992, after 10 years of
follow-up we confirmed 520 cases of prostate cancer, of whom 152
cases had adequate sample volume for IGF assays in 1997.
Circulating steroid hormone levels P. H. Gann, C. H. Hennekens, J.
Ma, C. Longcope, M. J. Stampfer, JNCI 88:1118 (1996). PSA (P. H.
Gann, C. H. Hennekens, M. J. Stampfer, JAMA 273:289 (1995), and CAG
polymorphisms of the androgen receptor gene (E. Giovannucci, M. J.
Stampfer, K. Krithivas, M. Brown, A. Brufsky, J. Talcott, C. H.
Hennekens, P. W. Kantoff. Proc. Natl. Acad. Sci. USA 94:3320 (1997)
had previously been measured in these cases from the same blood
samples originally collected in 1982 (Selection bias is minimal
here as it is unlikely that subjects returned blood samples or
provided adequate blood volume differentially based on any relation
between their IGF levels in 1982 and later development of prostate
cancer. Previous study has shown that cases who did and did not
provide blood samples were not appreciably different in their
baseline lifestyle characteristics (P. H. Gann, C. H. Hennekens, M.
J. Stampfer, JAMA 273:289 (1995). All assays reported in this study
are from blood specimens collected, on average, seven years (min. 6
months, max.=9.5 years) prior to clinical diagnosis of prostate
cancer.
[0051] We selected controls at random from those men who provided
blood and who had not reported a diagnosis of prostate cancer up to
the date of diagnosis of the case. We excluded those men without
adequate blood sample volume and those who had total or partial
prostatectomies by the time of the case diagnosis because they may
not have been fully at risk for the disease when the cases were
diagnosed. We matched one control to each case based on smoking
status (never, past, or current smoker), duration of follow-up, and
age within one year.
[0052] IGF-I, IGF-II, and IGFBP-3 were assayed using ELISAs with
reagents from DIAGNOSTIC SYSTEMS LABORATORY INC. (DSL Inc.,
Webster, Tex.) (This methodology was selected as it was shown to be
more reproducible and more appropriate for large numbers of samples
than an RIA technique we previously employed (M. Pollak, J.
Constantino, C. Polyochronakos, S. Blauer, H. Guyda, C. Redmond, B.
Fisher, R. Margolese. JNCI 82:1693 (1990). The IGF-I values
obtained by the ELISA were highly correlated (Pearson r=0.97) with
values obtained by RIA following acid chromatography. All assays
were carried out in a blinded fashion and quality control samples
were embedded within assay runs. Average intra-assay coefficients
of variation for IGF-I and IGF-II were 4.9% and 3.0%, respectively.
The IGFBP-3 assay employed does not cross-react with other IGF
binding proteins. Experiments with recombinant IGF-I and IGFBP-3
confirm that the assay detects IGFBP-3 whether or not it is
complexed to IGF-I in the presence or absence of the acid labile
subunit. The average intra-assay coefficient of variation for
IGFBP-3 was 9.0%. To evaluate the effect of our blood collection
methods on IGF-I levels, we compared IGF-I and IGFBP-3 levels in
blood samples which were processed and serum frozen immediately
after venipuncture (the usual collection and processing methods) to
samples, which were stored as heparinized whole blood for 24 and 36
hours before processing (mimicking our collection conditions). The
mean IGF-I and IGFBP-3 values were almost identical and the
interclass correlations between results of the two collection
methods were 0.98 for IGF-I and 0.96 for IGFBP-3, indicating that
our collection methods did not adversely affect sample integrity.
It has been shown that s single IGF-I measurement is representative
of levels over time (To examine how well a single measurement of
IGF-I represents levels overtime, we collected two blood samples
each from 16 people, eight weeks apart (time 1 and time 2). The
correlation between blood levels taken at time 1 and time 2 was
0.65; D. Goodman-Gruen, E. Barrett-Connor. Amer. J. Epidemiol.
145:970 (1997).
[0053] Paired t-tests were used to compare the means of IGF-I,
IGF-II, and IGFBP-3 between cases and controls. We then examined
the age-standardized (using five groups, 40-50, 51-55, 56-60,
61-65, 66-80) mean values of various predictors for prostate cancer
within quartiles of IGF-I among the controls. Conditional logistic
regression was used to analyze the associations between IGF and
prostate cancer adjusting for other possible risk factors for
prostate cancer--PSA, height, weight, body mass index, CAG
polymorphisms of the androgen receptor gene, and plasma androgen
levels, including estrogren, testosterone (T), dihydrotestosterone
(DHT), sex hormone binding globulin (SHBG), prolactin, and
3-alpha-androstanediol glucuronide (AAG) (P. H. Gann, C. H.
Hennekens, J. Ma, C. Longcope, M. J. Stampfer, JNCI 88:1118 (1996);
P. H. Gann, C. H. Hennekens, M. J. Stampfer, JAMA 273:289 (1995);
E. Giovannucci, M. J. Stampfer, K. Krithivas, M. Brown, A. Brufsky,
J. Talcott, C. H. Hennekens, P. W. Kantoff. Proc. Natl. Acad. Sci.
USA 94:3320 (1997). E. Giovannucci, E. B. Rimm, M. J. Stampfer, G.
A. Colditz, W. C. Willett. Cancer Epidemiology Biomarker, and
Prevention (in press); S-O Andersson, A. Wolk, R. Bergstrom, H-O
Adami, G. Engholm, A. Englund, O. Nyren. JNCI 89:385 (1997); B.
MacMahon and D. Trichopolous. Epidemiology Principles & Methods
(Little, Brown & Company, Boston, Mass. 1996), pp. 287-91; and
K. Rothman. Modern. Epidemiology (Little, Brown & Company,
Boston, Mass. 1986), pp. 250-7.
[0054] Because we hypothesized that IGFBP-3 reduces the bioactivity
of IGFs, we simultaneously adjusted for levels of both IGFs and
IGFBP-3. We estimated relative risk (RR) from the odds ratios and
computed 95 percent confidence intervals (CI) (K. Rothman. Modern
Epidemiology (Little, Brown & Company, Boston, Mass. 1986), pp.
250-7. In some analyses, we used unconditional logistic regression
models and adjusted for age (eight five-year categories) and
smoking (never, past, and current) in the models to make full use
of the data without restriction to the matched pairs. D. G.
Kleinbaum, L. L. Kupper, and H. Morgenstern. Epidemiologic Research
(Van Nostrand Reinhold, Boston, Mass. 1982), pp. 433-43. We
repeated the basic analyses examining only the high grade/stage
cases, only low grade/stage cases, and only cases occurring after
the first five years of follow-up, as prior studies have shown that
some risk factors for prostate cancer are stronger for high
grade/stage tumors P. H. Gann, C. H. Hennekens, J. Ma, C. Longcope,
M. J. Stampfer, JNCI 88:1118 (1996); E. Giovannucci, M. J.
Stampfer, K. Krithivas, M. Brown, A. Brufsky, J. Talcott, C. H.
Hennekens, P. W. Kantoff. Proc. Natl. Acad. Sci. USA 94:3320
(1997). We examined IGF-I and prostate cancer within age groups
(<=60, >60 at baseline) and smoking categories (never, past,
current) to consider potential interactions.
[0055] All exposures of interest and covariates, with the
exceptions of age and smoking, were analyzed in quartile groups
with the lowest quartile as the reference category. We tested
linear trends for statistical significance by assigning the medians
of each quartile as scores. B. Rosner. Fundamentals of
Biostatistics (Duxbury Press, Boston, Mass. 1995), pp. 604-7.
[0056] The mean level of IGF-I among the cases (269.4 ng/ml) was
significantly higher than among controls (248.9 ng/ml)(p=0.03).
Means of IGF-II and IGFBP-3 were similar among cases and controls
(p=0.85 and 0.95 respectively). Table 1 presents age-standardized
means of IGF-II, IGFBP-3, estradiol, T, DHT, SHBG, lycopene,
weight, height, body mass index, and medians of PSA among 152
controls, within quartiles of IGF-I. PSA and estradiol had weak
positive associations with IGF-I levels, while there was some
suggestion that lycopene levels were lower among men in the highest
quartile of IGF-I. There was no significant correlation between
IGF-I and any of these factors except IGF-II (r=0.5) and IGFBP-3
(r=0.6).
1TABLE 1 Age-standardized characteristics among 152 controls within
quartiles of IGF-I* IGF Quartile 1 2 3 4 IGF-I (ng/ml) 99.4-184.8
184.9-236.95 236.96-293.75 293.76-499.6 n 38 38 38 38 Age, years
(mean) 63.9 58.9 59.0 59.3 IGF-II, ng/ml (mean) 418 536 509 583
IGFBP-3, ng/ml (mean) 2234 2841 2829 3473 PSA.sup.+, ng/ml (median)
2.19 2.27 2.81 2.49 Lycopene, ng/ml (mean) 445 430 438 388
Estradiol, ng/ml (mean) 35.9 37.2 38.6 39.4 Testosterone, ng/ml
5.27 4.74 5.28 5.60 (mean) DHT.sup.+, ng/ml (mean) 0.41 0.41 0.44
0.43 SHBG.sup.+, nmol/L (mean) 27.9 20.9 24.8 21.7 Weight, kg
(mean) 77.1 78.6 78.7 77.4 Height, m (mean) 1.77 1.76 1.77 1.76
BMI.sup.+, kg/m.sup.2 (mean) 24.7 25.4 25.0 24.9 *Standardized
using 5 categories of age (40-50, 51-55, 56-60, 61-65, 66-80).
.sup.+PSA = prostate specific antigen, DHT = dihydrotestosterone,
SHBG = sex hormone binding globulin, BMI = body mass index.
[0057] IGF-I was significantly associated with prostate cancer risk
in a univariate analysis; men in the highest quartile had a
relative risk of 2.41 (95 percent CI 1.23-4.74) as compared to men
in the lowest quartile (Table 2). With further adjustment for
IGFBP-3, these men had more than four times the risk of prostate
cancer compared to the reference group (RR=4.32, 95 percent CI
1.76-10.6). IGF-II and IGFBP-3 were not associated with prostate
cancer risk when examined individually, but IGFBP-3 was inversely
associated with risk after controlling for IGF-I (RR for fourth vs.
first quartile 0.41, 95 percent CI 0.17-1.03). There was a
significant linear trend between IGF-I and prostate cancer risk,
especially after adjusting for IGFBP-3; a 100 ng/ml increase in
IGF-I corresponded to an approximate doubling of risk (RR=2.09 per
100 ng/ml increase, 95 percent CI 1.35-3.22). As anticipated, it
was important to consider the combined effects of IGF-I and IGFBP-3
simultaneously, and these were examined together in subsequent
analyses.
2TABLE 2 Relative risk of prostate cancer according to quartiles of
IGF-I, IGF-II, IGFBP-3. Quartiles 1 2 3 4 Trend p-value RR
associated with IGF-I Quartiles IGF-I* 1.00 1.32 1.81 2.41 0.01
(0.62-2.80)+ (0.92-3.56) (1.23-4.74) IGF-II 1.00 1.00 0.67 0.97
0.74 (0.54-1.84) (0.33-1.37) (0.48-1.95) IGFBP-3 1.00 0.92 0.69
1.07 0.96 (0.48-1.79) (0.33-1.44) (0.54-2.11) Simultaneous
adjustment for IGF-I or IGFBP-3 IGF-I 1.00 1.94 2.83 4.32 0.001
(0.83-4.56) (1.27-6.28) (1.76-10.6) IGFBP-3 1.00 0.50 0.33 0.41
0.09 (0.23-1.10) (0.14-0.82) (0.17-1.03) *n = 151 for cases, 1 case
missing of IGF-I. + 95% confidence intervals # Test for linear
trend calculated by assigning the medians of the quartiles as
scores.
[0058] IGF-I remained a significant independent predictor of
prostate cancer risk even after inclusion of quartiles of weight,
height, body mass index, androgen receptor CAG repeats, and various
circulating hormone levels (estradiol, T, DHT, SHBG, prolactin, and
AAG) in the multivariate models. Adding quartiles of PSA to the
model attenuated the association for IGF-I slightly, though the
results remained significant (RR=3.31, 95 percent CI 1.09-10.1 for
the fourth vs. first quartile, adjusting for IGFBP-3).
[0059] To investigate whether the observed associations between
IGF-I and prostate cancer could be due to increased IGF-I levels
among pre-clinical undiagnosed cases in 1982, we repeated the basic
analyses including only those men who were diagnosed five years or
more after the start of follow-up. With the remaining 125 cases and
152 controls, we observed very similar results to previous analyses
based on all cases and controls, and the effect of IGF-I adjusted
for PSA was also unaffected.
[0060] We compared the potential association between IGF-I and
prostate cancer risk among men with high grade/stage vs. low
grade/stage cancer at diagnosis and observed no significant
difference (RR for the fourth vs. first quartile of IGF-I 3.40 (95
percent CI 1.14-10.1) for high grade/stage cancers and 5.46 (95
percent CI 1.93-15.5) for low grade/stage cancers), suggesting that
IGF-I does not differentially influence the development of high vs.
low grade/stage tumors.
[0061] When we stratified subjects by the median case baseline age
of 60, the increased risk associated with IGF-I was stronger among
the older men. Men over the age of 60 and in the highest quartile
of IGF-I had a RR of 7.93 (95 percent CI 2.05-30.7), adjusting for
IGFBP-3, compared to men of similar age in the lowest quartile, and
we found no association between quartiles of IGF-I and risk among
the men age 60 or less. Among both older and younger men, however,
there was a significant linear relationship between RR and IGF-I
level (RR=1.83 per 100 ng/ml increase in IGF-I, p=0.047 for younger
men; RR=2.55 per 100 ng/ml increase in IGF-I, p=0.006 for older
men). We also examined IGF-I within strata of smoking and within
strata of six plasma androgens but observed no evidence of
interaction.
EXAMPLE 2
[0062] As PSA acts as an IGFBP protease in prostatic issue (P.
Cohen, H. C. Graves, D. M. Peehl, M. Kamarei, L. C. Biudice, R. G.
Rosenfeld. J. Clinical Endocrinology & Metabolism 75:1046
(1992), we also investigated possible interactions involving PSA.
There was no significant correlation between circulating PSA and
circulating IGFBP-3, consistent with the view that PSA is
enzymatically inert in the circulation. We classified men by
quartile of IGF-I and low (.ltoreq.4 ng/ml) vs. high (>4 ng/ml)
PSA level, creating eight mutually exclusive categories of IGF-I
and PSA. The low-PSA/lowest quartile of IGF-I category was used as
the reference group. Similar methods were used to examine potential
interactions between IGF-I and plasma androgens (using the median
among controls as the cutpoint for low and high androgen
levels).
[0063] Data in Table 3 confirm that as expected, men with elevated
baseline PSA were more likely to be subsequently diagnosed with
prostate cancer than those with PSA less than 4 ng/ml. More
importantly, serum IGF-I level was strongly related to risk of
developing prostate cancer even among men with a baseline PSA less
than 4 ng/ml (multivariate RR of clinical diagnosis during
follow-up increased from 1.00 to 4.57 across quartiles of IGF-I,
adjusted for IGFBP-3 and age, and smoking). Furthermore, assuming
that men with PSA greater than 4 ng/ml have a high likelihood of
harboring occult prostate cancer (P. H. Gann, C. H. Hennekens, M.
J. Stampfer, JAMA 273:289 (1995), the data provide evidence for a
substantial influence of IGF-I on the natural history of clinically
occult prostate cancer (multivariate RR of clinical diagnosis
during follow-up increased from 3.92 to 17.5 across quartiles of
IGF-I among men with elevated baseline PSA). These results suggest
men in the highest quartile of IGF-I have four and a half times
greater risk of prostate cancer than men in the lowest quartile
regardless of their PSA levels, and that a combined assessment of
IGF-I level and PSA may better predict subsequent prostate cancer
than a PSA measure alone.
3TABLE 3 IGF-I and risk of prostate cancer by category of
pre-diagnostic PSA level. RR* associated with IGF-I quartile PSA
level 1 2 3 4 .ltoreq.4 ng/ml 1.00.sup.+ 1.66 2.07 4.57 --
(0.70-3.92) (0.84-5.09) (1.79-11.6) >4 ng/ml 3.92 11 16 17.5
(1.01-15.3) (1.84-65.4) (4.08-62.6) (3.83-80.1) *Multivariate RR
adjusted for age (40-44, 45-49, 50-54, 55-59, 60-64, 65-69, 70-74,
75-80), smoking (never, past, current), and IGFBP-3 (quartiles)
+Reference group
[0064] Our data support the hypothesis that higher circulating
IGF-I levels are associated with higher rates of malignancy in the
prostate gland. Alternative explanations for the observations in
this study include measurement error, bias, and chance C. H.
Hennekens and J. E. Buring. Epidemiology in Medicine (Little, Brown
& Company, Boston, Mass. 1987), p. 243. We measured circulating
adult levels of IGF-I and IGFBP-3 using a single blood sample
drawn, on average, seven years prior to cancer diagnosis. It is
possible that another measure of IGF-I physiology (i.e. adolescent
or early adulthood mean IGF-I assessed over time, tissue IGF
bioactivity, or rate of cell turnover in the prostate gland) would
better capture the true etiologically relevant variable. To the
extent that our single measurement is a proxy for such a variable
and that the measurement errors are non-systematic and
proportionately equal among cases and controls, we have reduced the
observable variation between our cases and controls, and our
results are likely to underestimate the true association between
IGF-I and prostate cancer risk. K. Rothman. Ibid. pp. 84-9.
Measurement error in assessing prostate cancer outcome is minimal
given the physician study base and the histologic confirmation of
all cases, although there may be some under-ascertainment of
existing cases which would also lead to an underestimation of
effect.
[0065] A small case-control study (n=52 cases), in which blood
samples were drawn from men already diagnosed with prostate cancer
and healthy controls, showed a positive association of borderline
significance between IGF-I level and prostate cancer risk In a
small study (n=52), using blood samples collected post-diagnosis,
the authors reported a borderline significant association between
IGF-I and prostate cancer risk (RR=1.91, 95 percent CI 1.00-3.73
per 60 ng/ml increment of IGF-I, adjusted for age, height, body
mass index, years of schooling, SHBG, T, estradiol, DHT, and
dehydroepiandrosterone sulfate). C. S. Mantzoros, A. Tzonou, L. B.
Signorello, M. Stampfer, D. Trichopoulos, H-O Adami. British J. of
Cancer (in press). However, the retrospective design used in that
study could not rule out an effect of the cancer, or its treatment,
on IGF-I levels.
[0066] The association between circulating IGF-I level and risk of
prostate cancer is stronger than that of any previously reported
risk factor, including steroid hormone levels (P. H. Gann, C. H.
Hennekens, J. Ma, C. Longcope, M. J. Stampfer, JNCI 88:1118 (1996),
or anthropomorphic variables (E. Giovannucci, E. B. Rimm, M. J.
Stampfer, G. A. Colditz, W. C. Willett. Cancer Epidemiology
Biomarker, and Prevention (in press); S-O Andersson, A. Wolk, R.
Bergstrom, H-O Adami, G. Engholm, A. Englund, O. Nyren. JNCI 89:385
(1997); C. La Vecchia, E. Negri, F. Parazzini, P. Boyle, B.
D'Avanzo, F. Levi, A. Gentile, S. Franceschi. Intl. J. Cancer
45:275 (1990); P. Hebert, U. Ajani, N. R. Cook, I-M. Lee, K. S.
Chan, C. H. Hennekens. Cancer Causes & Control 8:591 (1997); G.
Tibblin, M. Eriksson, S. Cnattingius, A. Ekbom. Epidemiology 6:423
(1995). Prior reports showing a weak relationship between prostate
cancer risk and height (C. La Vecchia, E. Negri, F. Parazzini, P.
Boyle, B. D'Avanzo, F. Levi, A. Gentile, S. Franceschi. Intl. J.
Cancer 45:275 (1990); P. Hebert, U. Ajani, N. R. Cook, I-M. Lee, K.
S. Chan, C. H. Hennekens. Cancer Causes & Control 8:591 (1997),
are of particular interest in the context of our results, as IGF-I
levels have been reported to be correlated with height (A. Juul, P.
Bang, N. T. Hertel, K. Main, P. Dalgaard, K. Jorgensen, J. Muller,
K. Hall, N. E. Skakkebaek. J. Clinical Endocrinology &
Metabolism 78:744 (1994), and height may act as a weak surrogate
for IGF-I. Circulating IGF-I level, in turn, may be related to risk
because it represents a determinant of and/or a surrogate for
prostate tissue IGF bioactivity and/or cellular proliferation
rate.
[0067] In our study population, height was moderately associated
with prostate cancer risk, independent of weight, age, smoking,
IGF-I, and IGFBP-3 (RR=1.05 per cm increase in height, p=0.05).
However, we did not observe an association between IGF or IGFBP-3
and height in this study, possibly due to small sample size or
older age of the subjects. A small study (n=21 cases) that reported
high birth weight to be associated with a higher incidence of
prostate cancer, (G. Tibblin, M. Eriksson, S. Cnattingius, A.
Ekbom. Epidemiology 6:423 (1995), may also be consistent with our
observations, as there is evidence that birth weight is positively
correlated with IGF-I level (C. Lassarre, S. Hardouin, F. Daffos,
F. Forestier, F. Frankenne, M. Binoux. Pediatric Research 29:219
(1991).
[0068] Age-standardized prostate cancer incidence is increasing
even allowing for changes in ascertainment (P. Boyle, P.
Maisonneuve, P. Napalkow. Urology 46:47 (1995). There are grounds
for speculation that in certain human populations there is a trend
towards increasing IGF-I levels. The physiological basis for the
secular trend towards increased height over the past few
generations (H. Meredith. Am. J. Phys. Anthropol. 44:315 (1976),
remains unexplained, but this may be correlated with increased
IGF-I levels, particularly as severe malnutrition is less common,
and malnutrition is known to reduce IGF-I level (J. P. Thissen, J.
M. Keteislegen, L. B. Underwood. Endocrine Reviews 15:80
(1994).
[0069] Until now, reduction of androgen action has been the
principal strategy under investigation for prostate cancer
prevention (J. W. Aquilina, J. J. Lipsky, D. G. Bostwick. JNCI
89:689 (1997). Our data suggest that the HG/IGF-axis may also
deserve attention in this context. Reduction of IGF-I levels by
lifestyle modifications may not be possible, as a recent
cross-sectional study found IGF-I to be positively correlated with
younger age, male gender, and alcohol intake, but uncorrelated with
lifestyle-related factors such as body fat, lean body mass, current
smoking, physical activity, and use of common medications (D.
Goodman-Gruen, E. Barrett-Connor. Amer. J. Epidemiol. 145:970
(1997). However, pharmacological approaches to decreasing IGF-I
levels deserve investigation as risk reduction strategies
specifically targeted to those men who have elevated risk defined
on the basis of high IGF-I level.
[0070] The data also provide a rationale for examining the use of
this strategy in the treatment of early prostate cancer. Currently,
IGF-I levels may be reduced by the use of somatostatin analogues
(M. Pollak, C. Polchronakos, H. Guyda. Anticancer Research 9:889
(1989), or growth hormone releasing hormone antagonists (M.
Zarandi, J. E. Horvath, G. Halmos, J. Pinski, A. Nagy, K. Groot, Z.
Rekasi, A. V. Schally. Proc. Natl. Acad. Sci. USA 91:12298 (1994).
The former are well-tolerated agents commonly used in treatment of
acromegaly and are under investigation in other trials (M. Pollak,
J. Ingle, V. Suman, J. Kugler. Rationale for combined
antiestrogensomatostatin analogue therapy of breast cancer. In
Salmon, S. (Ed) Adiuvant Therapy of Cancer VIII, p. 145-153,
Lippincott, Philadelphia, 1997). In contrast, our results raise
concern that administration of growth hormone or IGF-I over long
periods, proposed for elderly men (D. Rudman, A. G. Feller, H. S.
Nagraj, G. A. Gorgans, P. Y. Lalitha, A. F. Goldberg, R. A.
Schlenker, L. Cohn, I. W. Rudmam, D. E. Mattson. NEJM 323:1 (1990),
may increase risk of prostate cancer.
[0071] The data reported here justify further epidemiological and
biological investigation of IGF-I and IGFBP-3 as predictors of
prostate cancer risk, as candidate intermediate endpoints for
chemoprevention studies, and as targets for future prevention and
therapeutic strategies.
* * * * *