This study is of participants originally diagnosed with adenocarcinoma of the prostate who have now developed mCRPC and who have progressed on therapy with abiraterone acetate plus prednisone/prednisolone (AA-P), apalutamide, darolutamide, or enzalutamide. Participants with treatment-emergent small-cell neuroendocrine prostate cancer (t-SCNC) assessed by the screening biopsy may be considered for this study. Participants must have confirmed prostate-specific antigen (PSA) progression per Prostate Cancer Clinical Trials Working Group (PCWG3) criteria. The primary hypothesis is that treatment with cetrelimab and apalutamide is safe and leads to improvement in the 12-week PSA response rate. The study consists of an Optional Pre-screening Period, Screening period (28 days prior to Cycle 1 Day 1), Treatment Period, End-of-Treatment Visit (performed after the last dose of study drug is administered), and Follow-up Period (participants will have Follow-up assessment every 12 weeks after the End-of-Treatment Visit). The efficacy, safety, and pharmacokinetics of cetrelimab in combination with apalutamide will be evaluated.
