Clinical Trials

Inclusion Criteria: 

• Participants willing to undergo all protocol-specified biopsies.
• Diagnosis of prostate adenocarcinoma as confirmed by the investigator.
• Combination 1: 
  • Must have determination of biomarker (BM) status for DNA-repair gene defects (DRD) (either BM positive [+] or BM negative [-]) by the sponsor's blood or tissue assay;
  • Participants must have measurable disease as defined by response evaluation criteria in solid tumors (RECIST) 1.1 (soft tissue lesion of greater than or equal to (≥) 10 millimeter (mm) in the long axis or extrapelvic lymph node of ≥ 15 mm in the short axis);
  • Must have previously received at least 1, but no more than 2, lines of novel androgen receptor (AR)-targeted therapy (that is, abiraterone acetate with prednisone, enzalutamide) for metastatic castration-resistant prostate cancer (mCRPC). Participants must have had at least 4 weeks of AR-targeted therapy.
• Combination 2:
  • Must be biomarker positive for DRD by either the sponsor's blood or tissue assay;
  • Must have progressed on 1 prior line of novel AR-targeted therapy (that is, abiraterone acetate with prednisone, enzalutamide) for mCRPC;
  • Prior treatment with taxane-based therapy and AR-targeted therapy outside of the mCRPC setting is allowed.

Exclusion Criteria: 

• Prior treatment with a poly (adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitor.
• History or current diagnosis of myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML).
• Active malignancy (exceptions: adequately treated basal cell or squamous cell skin cancer, superficial bladder cancer, or any other cancer in situ currently remission) less than or equal to (≤) 2 years prior to enrollment.
• Active infection requiring systemic therapy.
• Allergies, hypersensitivity, or intolerance to niraparib or the corresponding excipients.