Effective Control of Synchronous Male Breast and Prostate Cancer with Androgen Deprivation Therapy: A Case Report.

INTRODUCTION: Male breast cancer (BC) is a rare disease, accounting for less than 1% of all BCs, and its synchronous occurrence with prostate cancer (PC) is exceedingly rare. Male BC is generally managed according to treatment strategies established for female BC; however, the role of androgen receptor (AR) signaling and androgen deprivation therapy (ADT) in male BC remains unclear. In particular, the optimal treatment strategy for patients with synchronous male BC and PC has not been established, and it is unknown whether ADT for PC exerts therapeutic effects on AR-positive male BC. CASE PRESENTATION: A 74-year-old Japanese man was diagnosed with synchronous estrogen receptor (ER)-positive, AR-positive, luminal A-like male BC (cStage IIA) and metastatic PC (Stage IV). Given that the prognosis was primarily determined by metastatic PC, ADT consisting of a gonadotropin-releasing hormone antagonist and an AR antagonist was initiated prior to breast surgery. Notably, marked tumor regression was observed in the breast lesion during ADT. Subsequent mastectomy with sentinel lymph node biopsy revealed ypT1c pN0 disease. CONCLUSIONS: This case represents a rare clinical scenario in which standard ADT successfully controlled both metastatic PC and operable ER- and AR-positive male BC without upfront breast surgery. This case suggests that ADT may represent a potential initial therapeutic option for synchronous malignancies, particularly in patients in whom surgery is not feasible or can be deferred.