This is a Phase IV, randomized, open-label, 2-arm, multicenter study evaluating the efficacy and safety of olaparib in Chinese men with metastatic castration-resistant prostate cancer (mCRPC) who have failed prior treatment with a new hormonal agent (NHA) and have BRCA1/2 mutations. Approximately 42 subjects will be randomized in a 2:1 ratio to olaparib or to investigator's choice of NHA (enzalutamide or abiraterone acetate).