In the Trial of PARP Inhibition in Prostate Cancer (TOPARP-A) study, olaparib monotherapy had a composite response (defined as either objective response as per RECIST 1.1 with modified PCWG2 recommendations, a decrease in PSA of ≥ 50%, or a circulating tumor cell count conversion from ≥5 cells per 7·5 mL blood at baseline to <5 cells per 7·5 mL blood) of 88% with a median survival of 13.8 months in a small cohort of heavily pretreated patients with metastatic castrate-resistant prostate cancer (mCRPC) with HRR gene mutation (53). This evidence concerns the gene PARP1 and prostate cancer.