Study of Talazoparib With Enzalutamide in Men With DDR Gene Mutated mCSPC

The purpose of the study is to evaluate the safety and efficacy of talazoparib in combination with enzalutamide compared with placebo in combination with enzalutamide in participants with DDR-deficient mCSPC.

Inclusion Criteria: 1. Male participants at least 18 years of age at screening (20 years for Japan, 19 years for Republic of Korea). 2. Histologically or cytologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation, small cell or signet cell features. If the participant does not have a prior histological diagnosis, a baseline de novo biopsy must be used to confirm the diagnosis and may also be used to support biomarker analysis. 3. Confirmation of DDR gene mutation status by prospective or historical analysis (with sponsor pre-approval) of blood (liquid biopsy) and/or de novo or archival tumor tissue using FoundationOne Liquid CDx or FoundationOne CDx. 4. Willing to provide tumor tissue when available (de novo or archived) for retrospective molecular profiling analysis, if not already provided as part of inclusion criterion 3. 5. Unless prohibited by local regulations or ethics committee decision, consent to a saliva sample collection for retrospective sequencing of the same DDR genes tested on tumor tissue and blood (liquid biopsy), or a subset thereof, and to serve as a germline control in identifying tumor mutations. 6. Ongoing ADT with a GnRH agonist or antagonist for participants who have not undergone bilateral orchiectomy must be initiated before randomization and must continue throughout the study. 7. Metastatic prostate cancer documented by positive bone scan (for bone disease) or metastatic lesions on CT or MRI scan (for soft tissue). Participants whose disease spread is limited to regional pelvic lymph nodes are not eligible. Note: a finding of superscan at baseline is exclusionary. 8. Prior treatment of mCSPC with docetaxel is not permitted. 9. Treatment with estrogens, cyproterone acetate, or first-generation anti-androgens is allowed until randomization. 10. Other prior therapy allowed for mCSPC; ≤3 months of ADT (chemical or surgical) with or without approved NHT in mCSPC (ie, abiraterone + prednisone, apalutamide, or enzalutamide), if required prior to randomization, with no radiographic evidence of disease progression or rising PSA levels prior to Day 1. 11. Participant may have received palliative radiation or surgery for symptomatic control secondary to prostate cancer, which should have been completed at least 2 weeks prior to randomization. NOTE: Radical prostatectomy or definitive radiotherapy to the primary tumor for metastatic castration-sensitive prostate cancer with curative intent is not permitted. 12. ECOG performance status 0 or 1. 13. Adequate organ function within 28 days before the first study treatment on Day 1, defined by the following: * ANC ≥1500/µL, platelets ≥100,000/µL, or hemoglobin ≥9 g/dL (may not have received growth factors or blood transfusions within 14 days before obtaining the hematology laboratory tests at screening). * Total serum bilirubin \