A Study of Niraparib in Combination With Abiraterone Acetate and Prednisone Versus Abiraterone Acetate and Prednisone for the Treatment of Participants With Deleterious Germline or Somatic Homologous Recombination Repair (HRR) Gene-Mutated Metastatic Castration-Sensitive Prostate Cancer (mCSPC)

Breast Cancer Gene (BRCA) Subgroup: Radiographic Progression-free Survival (rPFS) Assessed by Investigator

rPFS: time interval from date of randomization to first date of radiographic progression as assessed by investigator or death due to any cause, whichever occurred first. rPFS was determined by: (1) progression of soft tissue lesions measured by computerized tomography (CT) or magnetic resonance imaging (MRI) per response evaluation criteria in solid tumors (RECIST) 1.1; (2) progression of bone lesions observed by bone scan per prostate cancer working group 3 (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. A confirmatory scan with \>=2 new lesions indicated progression; A confirmatory scan not showing \>=2 new lesions means no progression. If Week 8 scan shows \<2 new bone lesions compared to baseline, first scan with \>=2 new lesions compared to Week 8 scan indicated progression, when confirmed by a subsequent scan \>=6 weeks later.

Time frame: From date of randomization (Day -3 to Day 1) up to approximately 49 months

HRR Effector Subgroup: Radiographic Progression-free Survival (rPFS) Assessed by Investigator

rPFS: time interval from date of randomization to first date of radiographic progression as assessed by investigator or death due to any cause, whichever occurred first. rPFS was determined by: (1) progression of soft tissue lesions measured by CT or MRI per RECIST 1.1; (2) progression of bone lesions observed by bone scan per 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. A confirmatory scan with \>=2 new lesions indicated progression; A confirmatory scan not showing \>=2 new lesions means no progression. If Week 8 scan shows \<2 new bone lesions compared to baseline, first scan with \>=2 new lesions compared to Week 8 scan indicated progression, when confirmed by a subsequent scan \>=6 weeks later.

Time frame: From date of randomization (Day -3 to Day 1) up to approximately 49 months

All HRR: Radiographic Progression-free Survival (rPFS) Assessed by Investigator

rPFS: time interval from date of randomization to first date of radiographic progression as assessed by investigator or death due to any cause, whichever occurred first. rPFS was determined by: (1) progression of soft tissue lesions measured by CT or MRI per RECIST 1.1; (2) progression of bone lesions observed by bone scan per 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. A confirmatory scan with \>=2 new lesions indicated progression; A confirmatory scan not showing \>=2 new lesions means no progression. If Week 8 scan shows \<2 new bone lesions compared to baseline, first scan with \>=2 new lesions compared to Week 8 scan indicated progression, when confirmed by a subsequent scan \>=6 weeks later.

Time frame: From date of randomization (Day -3 to Day 1) up to approximately 49 months