Insulin-like growth factor I is not a useful marker of prostate cancer in men with elevated levels of prostate-specific antigen

High serum levels of insulin-like growth factor I (IGF-I) and low levels of IGF-binding protein-3 (IGFBP-3) have been shown to correlate: with increas ed prostate cancer risk. To evaluate this, IGF-I, IGFBP-3, and prostate-spe cific antigen (PSA) were measured in serum from 665 consecutive men (179 wi th prostate cancer), aged 55-67 yr, with elevated serum prostate-specific a ntigen (PSA; greater than or equal to4 mug/L) in a screening trial. Men in the highest quartile of IGF-I levels had an odds ratio (OR) for prostate ca ncer of 0.50 [95% confidence interval (CI) 0.26-0.97] when adjusting for se rum IGFBP-3. IGFBP-3 itself was not significantly associated with prostate cancer risk (OR, 1.24; 95% CI, 0.68-2.24). Prostate volume was larger in me n without than in those with prostate cancer (P < 0.001), and after adjustm ent for prostate volume, the negative association between serum IGF-I and p rostate cancer risk was no longer significant (OR, 0.57; 95% CI, 0.28-1.16) . In screen-positive men with elevated serum PSA, serum IGF-I is not a usef ul diagnostic test for prostate cancer, but it may be associated with benig n prostatic hyperplasia and enlargement.