The transforming growth factor alpha-epidermal growth factor receptor (EGFR) autocrine pathway has been implicated in prostate cancer cell growth. Amplification and/or overexpression of c-erbB-2, a receptor closely related to the EGFR, has been recently involved in prostate cancer progression. We investigated EGFR and c-erbB-2 expression in primary androgen-dependent and in advanced androgen-independent prostate cancer and their potential role as markers of disease progression.EGFR and c-erbB-2 expression were evaluated by immunohistochemistry in a consecutive series of 74 prostate cancer patients with the following characteristics: 29 patients (group 1) treated with radical prostatectomy; 29 patients (group 2) treated with luteinizing hormone-releasing hormone analogues and antiandrogen therapy followed by radical prostatectomy; and 16 patients with hormone-refractory metastatic disease. In all patients we evaluated: association between EGFR and/or c-erbB-2 expression and clinicopathological parameters; and disease-free survival according to EGFR and c-erbB-2 expression in univariate analysis (Kaplan-Meier product-limit method) and in multivariate analysis (Cox proportional hazards regression model).EGFR expression was found in 12 of 29 (41.4%) group 1 patients, in 22 of 29 (75.9%) group 2 patients (P < 0.0005), and in 16 of 16 (100%) metastatic patients (P < 0.005), whereas c-erbB-2 expression was found in 11 of 29 (37.9%) group 1, in 10 of 29 (34.5%) group 2 patients, and in 9 of 16 (56.3%) metastatic patients. A significant association was found between EGFR expression and a high Gleason score (P < 0.01) and between EGFR expression and higher serum prostate-specific antigen values (P < 0.02) in all groups of patients. Among the 58 patients treated with radical prostatectomy, 23 of 34 EGFR-positive patients (67.6%) relapsed, whereas only 2 of 24 EGFR-negative patients (8.3%) relapsed (P < 0.00004). c-erbB-2 expression did not significantly correlate with disease relapse (P = 0.07). In a Cox multivariate analysis, the only parameter with an independent prognostic effect on disease-free survival was EGFR expression (relative hazard, 11.23; P = 0.0014).EGFR expression increases during the natural history of prostate cancer. Correlation with disease progression and hormone-refractory disease suggests that EGFR-targeted drugs could be of therapeutic relevance in prostate cancer.