Prostate cancer recurring as small‐cell carcinoma with a BRCA2 somatic mutation

INTRODUCTION: Small‐cell carcinoma of the prostate has a poor prognosis, and treatment options for the refractory disease are unclear. CASE PRESENTATION: A 68‐year‐old man with prostate cancer was referred to our hospital. He was treated with combined androgen blockade (bicalutamide and degarelix acetate). The disease progressed to castration‐resistant prostate cancer, but with additional treatment, prostate‐specific antigen levels remained below 0.02 ng/mL. However, computed tomography revealed enlarged right inguinal lymph nodes; moreover, his neuron‐specific enolase levels were elevated. Histopathologic analysis of a biopsied lymph node confirmed small‐cell carcinoma. After administering cytotoxic chemotherapy (etoposide plus cisplatin and amrubicin), the patient temporarily improved before relapsing. After genetic testing of the biopsy specimen revealed a BRCA2 deletion, we administered the oral PARP‐2 inhibitor olaparib, which has achieved partial remission for 8 months. CONCLUSION: PARP‐2 inhibition may improve the survival of patients with BRCA2‐positive small‐cell carcinoma of the prostate.