Insulin-like growth factor-I (IGF-I) and IGF binding protein-3 as predictors of advanced-stage prostate cancer

BACKGROUND: Plasma levels of insulin-like growth factor-I (IGF-I) have been associated with the risk of prostate cancer. However, the association of IGF-I with specific tumor stage and grade at diagnosis, which correlate with risk of recurrence and mortality, has not been studied rigorously. To determine whether plasma levels of IGF-I and its main circulating binding protein, IGF binding protein-3 (IGFBP-3), predict more aggressive forms of prostate cancer, we investigated the association between plasma levels of each and specific stages and grades of prostate cancer. METHODS: We examined 530 case patients and 534 control subjects in a nested case-control study in the prospective Physicians' Health Study. Patients with prostate cancer diagnosed from 1982 through 1995 were matched to control subjects by age and smoking status. IGF-I and IGFBP-3 were measured in prospectively collected plasma samples. Conditional logistic regression models were used to estimate the relative risks (RRs) for prostate cancer associated with IGF-I and IGFBP-3, stratified on grade (Gleason score > or = 7 versus