A Clinical Study Evaluating The Benefit of Adding Rucaparib to Enzalutamide for Men With Metastatic Prostate Cancer That Has Become Resistant To Testosterone-Deprivation Therapy

Inclusion Criteria: * Histologic/cytologic documentation of prostate adenocarcinoma * Adequate archival tumor specimen or archival slides must be available to be tested as part of the trial screening (most recent metastatic site biopsy preferred, but primary prostate biopsy allowed if metastatic biopsy is not available or inadequate. A new biopsy is not required for pre-registration in the trial as long as sufficient archival tissue is available). Due to significant variability between tests, results from an existing targeted next-generation exome sequencing test may not be used for this trial * Progressive disease must be demonstrated at study entry while the patient is on continuous androgen deprivation therapy (ADT) or status post orchiectomy. Progressive disease is defined as one or more of the following criteria: * PSA progression, defined by at least 2 consecutive rising PSA values at a minimum of 1-week intervals with the most recent PSA value being 1.0 ng/mL or higher, if confirmed PSA rise is the only indication of progression. Patients who received an anti-androgen must have PSA progression after withdrawal of anti-androgen therapy (\>=4 weeks since last flutamide, bicalutamide or nilutamide, apalutamide or darolutamide) * Radiographic progression per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 for soft tissue lesions * Bone metastasis progression per Prostate Cancer Working Group 3 (PCWG3) criteria * Measurable or non-measurable metastatic dis…