SAN FRANCISCO, CALIFORNIA. Insulin-like growth factor-1 (IGF-1) is a potent stimulator of prostate cancer cell growth. It is mostly found in the blood bound to its carrier, IGF binding protein-3 (IGFBP-3). Only the unbound form of IGF-1 has a cancer promoting effect.
A team of researchers from Harvard Medical School and the University of California has just completed a major study aimed at determining if IGF-1 and IGFBP-3 levels can predict the risk of developing advanced stage prostate cancer. Their study involved 530 patients with prostate cancer and 534 controls matched for sex and smoking status. All participants were part of the Physicians' Health Study and were between the ages of 40 and 84 years at enrollment in 1982. Almost 15,000 of the men provided blood samples that were stored for future analysis. By the end of 1995, 786 cases of prostate cancer had been diagnosed among the 14,916 participants (5.2%). Sufficient blood plasma for IGF-1 and IGFBP-3 analysis was available for 530 of the cases and their matched 534 controls. The diagnosis of prostate cancer was made an average of 9 years after the drawing of the blood samples.
The researchers observed a strong association between IGF-1 and IGFBP-3 levels and the risk of advanced
prostate cancer, but found no association with early stage disease. They found that men with IGF levels in
the highest quartile had a 5.1 times higher risk of later developing advanced stage prostate cancer than did
men in the lowest quartile. Men with IGFBP-3 levels in the highest quartile, on the other hand, had a 5
times lower risk of later advanced stage cancer (OR=0.2). Advanced stage prostate cancer was defined as
stage C (extraprostatic, but no evidence of distant metastases) or stage D (distant metastatic or fatal).
About 10% of the total 530 cases were stage D. The researchers speculate that IGF-1 not only stimulates
tumour initiation and growth, but may also facilitate invasion and metastases. They conclude that
measurement of IGF-1 and IGFBP-3 levels may predict the risk of advanced stage prostate cancer years
before the cancer is actually diagnosed and may thus be helpful in aiding decision making about