BRCA2 Frameshift Mutation in de novo Small-Cell Neuroendocrine Carcinoma of the Prostate: A Case Report

A 66-year-old male was diagnosed with cT4N0M1b small-cell neuroendocrine carcinoma of the prostate. Four months after the administration of combined androgen blockade, multiple novel metastatic regions in the lung and liver and progression of bone metastasis were observed. The patient was referred to our hospital because of biochemical and radiographic progression after four cycles of docetaxel as a first-line therapy for castration-resistant prostate cancer. Transurethral resection of the prostate and hepatic biopsy revealed small-cell carcinoma with positive expression of neuroendocrine markers. The FoundationOne CDx next-generation sequencing test revealed several pathogenic variants, including BRCA2 (W1692fs*3), KEAP1 (R320W), and TP53 (C2385) mutation. After four cycles of chemotherapy with carboplatin plus etoposide (CE), the metastatic regions regressed markedly. The prostate-specific antigen (PSA) and neuron-specific enolase (NSE) level decreased by 96.9% and 91.6%, respectively. However, 2 months after the completion of four cycles of CE, elevation of tumor marker levels, and re-growth of the metastatic regions were observed. Although olaparib, a poly (ADP-ribose) polymerase inhibitor (PARPi), achieved a 45.2% decrease in NSE, the patient rejected to continue therapy because of G2 adverse events. After receiving an additional two cycles of CE and one cycle of cabazitaxel, the patient died because of cancer progression 24 months after the initial treatment for prostate cancer. Here, we present a case of BRCA2-altered small-cell neuroendocrine prostate cancer treated with both platinum-containing chemotherapy and PARPi. Both therapies achieved an initial response; however, durable responses were not obtained. Additional discussion regarding the optimal treatment strategy for BRCA-altered small-cell/neuroendocrine prostate cancer is required.