Male Breast Metastasis: A Case of Treatment-Emergent Neuroendocrine Prostate Cancer.

Treatment-emergent transformed neuroendocrine prostate cancer (NEPC) is a highly aggressive type of prostate cancer that may arise from typical adenocarcinoma of the prostate, which is associated with rapidly progressive disease involving visceral sites and refractoriness to hormonal therapy. We present the case of a 74-year old male with a known history of stable prostate adenocarcinoma treated with transurethral prostate resection, local radiotherapy (RT), and androgen deprivation therapy (ADT) in 2020 who presented to the emergency room with complaints of shoulder and anterior chest pain, dyspnoea, and fatigue. Upon examination, a solid, adherent breast mass and infra-clavicular adenopathy were palpable. Thoracic computed tomography (CT) scan showed adenopathies in multiple thoracic chains, bilateral pulmonary nodular opacities, multiple osteolytic lesions, and bilateral enlargement of retro areolar tissue. A staging CT scan revealed further hepatic and penile lesions. Breast mass biopsy was compatible with small cell neuroendocrine cancer. Biopsies of the prostate, penis, lymph nodes, and bronchus were also performed. Histology of the prostate showed focal infiltration by the known adenocarcinoma while all others documented extensive infiltration by neuroendocrine carcinoma, whose morphology and immunohistochemical profile were identical to that of the breast. This case highlights the challenges a diagnosis of neuroendocrine prostate cancer might pose, and the aggressiveness of this type of cancer, which frequently presents with advanced disease and is associated with poor outcomes.