Background We examined whether human epidermal growth factor-2(HER-2) overexpression could be a useful marker of outcome after hormone therapy in patients with M1b prostate cancer (PC). Subjects and Methods The subjects were 102 patients who were diagnosed with M1b PC at Aichi Medical University Hospital. HER-2 expression was determined by immunohistochemical (IHC) staining using initial needle biopsy specimens for diagnosis. The results were classified into four grades (0, 1+, 2+, 3+), and scores of 1+ or greater were considered overexpression and defined as positive. Results The results showed a rating of 0 in 72 subjects, 1+ in 10, 2+ in 14, and 3+ in 6; 30 subjects (29.4%) were classified as HER-2 positive. Comparison of clinical data of HER-2 positive and negative subjects obtained at baseline revealed many of the subjects with high-grade tumors by Gleason score were HER-2 positive (P = 0.030). The prostate-specific antigen (PSA) relapse was observed in 76 subjects and cause-specific death occurred in 44. A significant difference was observed only in the item HER-2 (negative vs. positive) by multivariate Cox proportional hazard analysis. The 5-year PSA relapse-free rate was 0% in subjects with HER-2 positive (26/30), and 43.9% in subjects with HER-2 negative (50/72, P = 0.0192). The 5-year cause-specific survival rate was 40.9% in subjects with HER-2 positive (30/102), and 67.3% in subjects with HER-2 negative (72/102, P = 0.0301). Conclusion HER-2 overexpression as determined by IHC staining using needle biopsy specimens for diagnosis with M1b PC is a significant prognostic factor for PSA relapse after hormone therapy and unfavorable outcome.
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