Prophylactic Breast Irradiation for Prevention of Bicalutamide-induced Painful Gynecomastia in Patients with Low- and Intermediate-risk Prostate Cancer.

Background: Bicalutamide monotherapy (BMT) is an option for androgen deprivation therapy (ADT) in patients with low- and intermediate-risk prostate cancer (LIR-PC). Painful gynecomastia (PG) is a common side effect of BMT. Few therapeutic options are available for preventing BMT-induced PG.
Objectives: To assess the efficacy and side effects of single fraction (SF) prophylactic breast irradiation (PBI) to prevent painful gynecomastia (PG) in patients LIR-PC treated with BMT.
Methods: We reviewed the results of bilateral PBI in a prospective cohort of LIR-PC patients who received 150 mg bicalutamide daily as a first-line treatment for at least 12 months. A single fraction of 8 Gy was administered to both breasts by a stationary field of 10 × 10 cm, using 10-15 MeV electron beam. PBI was commenced on the same day as BMT, but prior to the first dose of bicalutamide. A radiotherapy treatment plan was designed to cover breast tissue by the 90% isodose line. Subsequent monthly physical examinations were scheduled for all patients during the first year of BMT to evaluate any PG symptoms.
Results: Seventy-six patients received BMT and PBI, 80% (61/76) showed no signs of PG; 20% (15/76) experienced mild gynecomastia. The main adverse effect of PBI was grade 1 radiation dermatitis.
Conclusions: PBI using a SF of 8 Gy is an effective, safe, and low-cost strategy for the prevention of BMT-induced PG in LIR-PC patients.