Prophylactic breast irradiation with a single dose of electron beam radiotherapy (10 Gy) significantly reduces the incidence of bicalutamide-induced gynecomastia.

Purpose: To evaluate the efficacy and tolerability of prophylactic breast irradiation in reducing the incidence and severity of bicalutamide-induced gynecomastia and breast pain.

Methods And Materials: In all, 106 men with prostate cancer (T1b-T4/Nx/M0) and no current gynecomastia/breast pain were enrolled in this randomized, sham-controlled, double-blind, parallel-group multicenter trial. Patients received either a single dose of electron beam radiotherapy (10 Gy) or sham radiotherapy. Bicalutamide (Casodex) 150 mg/day was administered for 12 months from the day of radiotherapy. Every 3 months, patients underwent physical examination and questioning about gynecomastia and breast pain.

Results: The incidence of investigator-assessed gynecomastia was significantly lower with radiotherapy vs. sham radiotherapy (52% vs. 85%; odds ratio [OR], 0.13; 95% confidence interval [CI], 0.04, 0.38; p < 0.001); direct questioning showed similar results. Fewer radiotherapy patients had >/=5 cm gynecomastia (measured by calipers; 11.5% vs. 50.0% for sham radiotherapy), and fewer cases were moderate-to-severe in intensity (21% vs. 48%). Similar proportions of radiotherapy and sham radiotherapy patients experienced breast pain (83% vs. 91%; OR, 0.25; 95% CI, 0.05, 1.27; p = 0.221); patients receiving radiotherapy experienced some reduction in its severity (OR, 0.44; 95% CI, 0.20, 0.97; p = 0.0429).

Conclusions: Prophylactic breast irradiation is an effective and well-tolerated strategy for prevention of bicalutamide-induced gynecomastia.