Background: Gynaecomastia and breast pain are frequent adverse events with bicalutamide monotherapy, and might cause some patients to withdraw from treatment. We aimed to compare tamoxifen with radiotherapy for prevention and treatment of gynaecomastia, breast pain, or both during bicalutamide monotherapy for prostate cancer. Methods: 51 patients were randomly assigned to 150 mg bicalutamide per day, 50 patients to 150 mg bicalutamide per day and to 10 mg tamoxifen per day for 24 weeks, and 50 patients to 150 mg bicalutamide per day and radiotherapy (one 12-Gy fraction on the day of starting bicalutamide). 35 of the 51 patients allocated bicalutamide alone developed gynaecomastia or breast pain and were subsequently randomly allocated to tamoxifen (n=17) or radiotherapy (n=18) soon after symptoms started (median 180 days, range 160-195). Gynaecomastia and breast pain were assessed once a month. Severity of gynaecomastia was scored on the basis of the largest diameter. Breast pain was scored as none, mild, moderate, or severe. The primary outcome was frequency of gynaecomastia or breast pain; secondary outcomes were safety and tolerability, relapse-free survival, as assessed by concentration of prostate specific antigen, and quality of life. Analyses were by intention to treat. Results: 35 of 51 patients assigned bicalutamide alone developed gynaecomastia, compared with four of 50 assigned bicalutamide and tamoxifen (odds ratio [OR] 0·1 [95% CI 0·08-0·12], p=0·0009), and with 17 of 50 assigned bicalutamide and radiotherapy (0·51 [0·47-0·54], p=0·008). Breast pain was seen in 29 of 51 patients allocated bicalutamide alone, compared with three allocated bicalutamide and tamoxifen (0·1 [0·07-0·11], p=0·009), and with 15 allocated bicalutamide and radiotherapy (0·43 [0·40-0·45], p=0·02) In 35 patients assigned bicalutamide alone who subsequently developed gynaecomastia, breast pain, or both, tamoxifen significantly reduced the frequency of gynaecomastia (0·2 [0·18-0·22], p=0·02). Interpretation: Antioestrogen treatment with tamoxifen could help patients with prostate cancer to tolerate the hypergonadotropic effects of bicalutamide monotherapy.
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