Does Prophylactic Radiation Therapy to Avoid Gynecomastia in Patients With Prostate Cancer Increase the Risk of Breast Cancer?

Purpose: Prostate cancer (PC) patients who undergo antiandrogen monotherapy are offered prophylactic radiation therapy (PRT) to the breast buds to avoid gynecomastia. The aim of the present study was to evaluate whether the risk of breast cancer (BC) in men with PC as their first cancer diagnosis was influenced by PRT.

Methods And Materials: From the Norwegian Cancer Registry, we collected data from all patients with PC as their first cancer diagnosis from 1997 to 2014. We registered all RT given to the patients in the same period and the occurrence of BC diagnosed ≥3 months after the PC diagnosis. The histopathologic diagnoses of all BC cases were collected. Subdistribution hazard ratios for the risk of BC in the PRT and non-PRT groups were estimated. A standardized incidence ratio for BC was calculated by comparing our cohort to the standard male population.

Results: We analyzed 59,169 patients with PC, of whom 7864 (13.3%) had received PRT. The median follow-up time was 4 years. Of the 12 men with a diagnosis of BC, 3 had received PRT, and 2 of the 3 were phyllodes tumors. The risk of BC was not significantly different statistically for the patients given PRT compared with the non-PRT group (subdistribution hazard ratio 1.62, 95% confidence interval 0.41-5.62, adjusted for age and time of diagnosis). The standardized incidence ratio was 0.996 (95% confidence interval 0.57-1.75).

Conclusions: In this registry-based study, we did not find an increased risk of BC in PC patients who received PRT. The number of BC cases in our study was low, and the risk of secondary BC after PRT seems to be negligible. The incidence of BC could, however, increase with additional follow-up. Also, 2 patients who had received PRT developed a malignant phyllodes tumor, an extremely rare type of BC associated with gynecomastia.