PRIMARY OBJECTIVE:~I. To determine the efficacy of abiraterone acetate/niraparib (CJNJ-67652000 [niraparib/abiraterone acetate fixed-dose combination]) and prednisone as assessed by prostate-specific antigen decline >= 50% (PSA50) response rate in patients with metastatic castrate-resistant prostate cancer (mCRPC) who have failed prior treatment with androgen receptor (AR)-targeted therapy and have a qualifying, deleterious SPOP mutation.~SECONDARY OBJECTIVES:~I. To assess the radiologic progression free survival (rPFS) of CJNJ-67652000 (niraparib/abiraterone acetate fixed-dose combination) and prednisone treatment in patients with mCRPC who have failed prior treatment with AR-targeted therapy and have a qualifying, deleterious SPOP mutation.~II. To assess best radiographic response using Prostate Cancer Working Group 3 (PCWG3) criteria.~III. To assess time to prostate specific antigen (PSA) progression. IV. To assess safety and tolerability using National Cancer Institute (NCI) Common Toxicity Criteria Version 5.0.~CORRELATIVE RESEARCH OBJECTIVES:~I. To explore the landscape of genomic alterations occurring after use of CJNJ-67652000 (niraparib/abiraterone acetate fixed-dose combination) and prednisone.~II. To use blood, tissue, or organoid lines for identifying predictive biomarkers of response, investigating drug resistance mechanisms, and for future drug efficacy studies.~III. To explore the relationship of other genomic alterations in the tumor tissue with overall response rate (ORR) and disease progression.~OUTLINE:~Patients receive CJNJ-67652000 orally (PO) and prednisone PO on study. Patients also undergo blood specimen collection, computed tomography (CT) or magnetic resonance imaging (MRI), and bone scan throughout the trial.
This phase II trial tests how well abiraterone acetate/niraparib (CJNJ-67652000 [niraparib/abiraterone acetate fixed-dose combination]) and prednisone works in treating patients with castration-resistant prostate cancer that has spread from where it first started (primary site) to other places in the body (metastatic) and who have a mutation in the SPOP gene. CJNJ-67652000 (niraparib/abiraterone acetate fixed-dose combination) is a drug which stops certain cancer cells from being able to repair themselves from damage, leading to the death of the cancer cell. Prednisone is in a class of medications called corticosteroids. It is used to reduce inflammation and lower the body's immune response to help lessen the side effects of chemotherapy drugs. Giving CJNJ-67652000 and prednisone may kill more tumor cells in patients with metastatic prostate cancer than giving these drugs alone.