PHILADELPHIABlack men have reduced levels of insulin-like
growth factor binding protein 3 (IGF-BP3), compared to white men, and
this may be a factor in the higher prostate cancer rates seen in this
population, researchers reported at the 90th annual meeting of the
American Association for Cancer Research (AACR) in Philadelphia.
A number of studies have provided evidence for an association between
alterations in the plasma levels of insulin-like growth factor-1
(IGF-1) and IGF-BP3 in prostate cancer risk. IGF-1, for example, has
been shown to stimulate prostate cells to grow. IGF-BP3 binds to
IGF-1 in the blood, and lower levels of the binding protein could
result in more unbound (free) IGF-1. It is thought that only free
IGF-1 is available (or free) to exert its growth effects
Our goals were to determine the plasma levels of these proteins
in a group of men at increased risk for developing prostate cancer
and to investigate the relationship between these levels and their
race, age, and smoking status, said James V. Tricoli, PhD, of
the Fox Chase Cancer Center.
The study group consisted of 105 men age 35 to 69 with no personal
history of prostate cancer but at least one first-degree relative
diagnosed with the disease. An enzyme-linked immunoadsorbent assay
(ELISA) was used to quantitate plasma levels of IGF-1 and IGF-BP3.
Significant Decrease in IGF-BP3
The study showed that the mean plasma level of IGF-1 was not
significantly different between black men (162.3 ng/mL) and white men
(172.1 ng/mL) (P = .415). However, the mean plasma level of IGF-BP3
was lower in black men (2,789 ng/mL) than in white men (3,216 ng/ml),
and this decrease was highly significant (P = .0045)
This supports a hypothesis that lower IGF-BP3 levels, resulting in
greater IGF-1 bioavailability, may be partially responsible for the
increased risk of prostate cancer in black men.
Exactly how increased levels of free IGF-1 might
contribute to the development of prostate cancer and the clinical
implications of lower IGF-BP3 levels will require further study,
Dr. Tricoli said. The trial, which has since been published
in Urology (July 1999), also showed significantly lower IGF-1 and
IGF-BP3 plasma levels in smokers vs nonsmokers.
For reasons that we do not completely understand, black men
have a roughly twofold greater incidence of prostate cancer than
white men, Dr. Tricoli said at a press conference. He cautioned
that, at this point, we have no solid evidence that the plasma
level of IGF-BP3 is an indicator for the presence of prostate cancer,
or a predictor for the occurrence of prostate cancer, in blacks or in
any other population of men.
Dr. Tricoli noted that the Fox Chase Cancer Center researchers are
currently conducting studies aimed at determining whether lower
levels of IGF-BP3 can predict the earlier onset of prostate cancer in
high-risk men and examining how this protein is involved in the basic
biology of the disease.