A Study of Niraparib in Combination With Abiraterone Acetate and Prednisone Versus Abiraterone Acetate and Prednisone for Treatment of Participants With Metastatic Prostate Cancer

Cohort 1: Radiographic Progression-Free Survival (rPFS) as Assessed by Blinded Independent Central Review (BICR)

As per BICR, rPFS is time interval from the date of randomization to radiographic progression or death, whichever occurred first. Radiographic progression was determined by: (1) progression of soft tissue lesions measured by computerized tomography (CT) or magnetic resonance imaging (MRI) as per response evaluation criteria in solid tumors (RECIST) 1.1; (2) Progression of bone lesions observed by bone scan based on prostate cancer working group 3 (PCWG3) criteria. PCWG3 criteria: bone progression was confirmed by subsequent scan greater than or equal to (\>=) 6 weeks later. Week 8 scan was baseline to which all subsequent scans were compared to determine progression. Confirmatory scan \>=2 new lesions indicate progression; scan does not show \>=2 new lesions means no progression. If Week 8 scan less than (\<) 2 new bone lesions compared to baseline, the initial scan \>=2 new lesions compared to Week 8 scan indicates progression if confirmed by subsequent scan \>=6 weeks later.

Time frame: Up to 32 months

Cohort 1 Breast Cancer Gene (BRCA) Subgroup: Radiographic Progression-Free Survival (rPFS) as Assessed by Blinded Independent Central Review (BICR)

As per BICR, rPFS is time interval from the date of randomization to radiographic progression or death, whichever occurred first. Radiographic progression was determined by: (1) progression of soft tissue lesions measured by CT or MRI as per RECIST 1.1; (2) Progression of bone lesions observed by bone scan based on PCWG3 criteria. PCWG3 criteria: bone progression was confirmed by subsequent scan \>=6 weeks later. Week 8 scan was baseline to which all subsequent scans were compared to determine progression. Confirmatory scan \>=2 new lesions indicate progression; scan does not show \>=2 new lesions means no progression. If Week 8 scan \<2 new bone lesions compared to baseline, the initial scan \>=2 new lesions compared to Week 8 scan indicates progression if confirmed by subsequent scan \>=6 weeks later.

Time frame: Up to 32 months