Inclusion Criteria:

          -  Have signed an Institutional Review Board (IRB)/Independent Ethics Committee (IEC)
             approved informed consent form prior to any study-specific evaluation

          -  Be ≥18 yrs of age at the time the informed consent form is signed

          -  Be either AR-directed therapy-naive or have received 1-2 lines of AR-directed therapy
             in the castration-resistant setting.

          -  Adequate organ function

          -  ECOG 0 or 1

          -  Have a histologically or cytologically confirmed adenocarcinoma or poorly
             differentiated carcinoma of the prostate that is metastatic

          -  Be surgically or medically castrated, with serum testosterone levels of ≤ 50 ng/dL
             (1.73 nM)

          -  Have disease progression after initiation of most recent therapy

        Exclusion Criteria:

          -  Active second malignancy, with the exception of curatively treated non melanoma skin
             cancer, carcinoma in situ, or superficial bladder cancer

          -  Have received greater than 2 previous lines of chemotherapy for mCRPC

          -  Prior treatment with any PARP inhibitor

          -  Symptomatic and/or untreated central nervous system metastases

          -  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

          -  Spinal cord compression, symptomatic and/or untreated central nervous system (CNS)
             metastases or leptomeningeal disease. Patients with asymptomatic previously treated
             CNS metastases are eligible provided they have been clinically stable for at least 4
             weeks

          -  Any clinically significant cardiovascular disease

          -  Taking any concomitant medications or herbs that could interfere or interact with the
             study drug