Epidemiologic studies have shown that growth factors and inflammatory mechanisms may affect breast cancer risk and prognosis. The present analysis on 110 postmenopausal breast cancer patients tested if serum insulin-like growth factor I (IGF-I), platelet-derived growth factor (PDGF), fructosamine, and C-reactive protein, a serum marker of inflammation, are associated with breast cancer relapse. The risk of adverse events after 5.5 years of follow-up was examined by Cox proportional hazards modeling, controlling for hormone receptor status, stage at diagnosis, and for body weight and serum testosterone level, which were known to significantly affect prognosis. PDGF and, to a lesser extent, IGF-I were positively but not significantly associated with the risk of breast cancer recurrence. By combining PDGF and IGF-I, however, the adjusted hazard ratio of recurrence among the women with both PDGF and IGF-I levels > their median values (respectively, 9.3 and 174.4 ng/mL) was 6.4 (95% confidence interval, 1.5-26.7) compared with the women with PDGF and IGF-I levels < or = their median values. Fructosamine and C-reactive protein were not associated with recurrences. The results suggest that PDGF may be an important prognostic factor for breast cancer and that IGF-I may increase the risk of recurrence in the presence of high PDGF levels.