Two Japanese patients with metastatic castration-resistant prostate cancer with somatic biallelic BRCA2 loss and RB1 splice site variant or loss who responded to Poly-ADP-ribose polymerase inhibitor: A case report.

We treated two patients with metastatic castration-resistant prostate cancer (mCRPC) who achieved a response duration of more than 12 months with Poly-ADP-ribose polymerase inhibitor (PARPi). Case 1 was a patient in his 60s with lung metastases, and case 2 was in his 70s and presented liver metastases. Genetic tests (FoundationOne(®) CDx) were performed. Both patients had somatic biallelic BRCA2 loss, together with RB1 splice site variant (NM_000321.3:c.2489 + 1G > C) or RB1 loss. After PARPi administration, their metastatic sites had shrunk enough to keep partial response. These cases suggested that patients with mCRPC with biallelic BRCA2 loss and the RB1 splice site variant or loss may have remarkable response to PARPi.