Inclusion Criteria:

1. Be 18 years old at the time the informed consent is signed
2. Have a histologically or cytologically confirmed adenocarcinoma or poorly differentiated carcinoma of the prostate that is metastatic
3. Be surgically or medically castrated, with serum testosterone levels of ≤ 50 ng/dL (1.73 nM)
4. Be eligible for treatment with physician's choice of comparator treatment (abiraterone acetate, enzalutamide or docetaxel)
5. Experienced disease progression after having received 1 prior next generation androgen receptor-targeted therapy
6. Have a deleterious mutation in a BRCA1/2 or ATM gene

Exclusion Criteria:

1. Active second malignancy, with the exception of curatively treated non melanoma skin cancer, carcinoma in situ, or superficial bladder cancer
2. Prior treatment with any PARP inhibitor
3. Prior treatment with chemotherapy for metastatic castration-resistant prostate cancer
4. Symptomatic and/or untreated central nervous system metastases
5. Pre-existing duodenal stent and/or any gastrointestinal disorder or defect that would, in the opinion of the investigator, interfere with absorption of study drug