REGN21353 Alone or in Combination With Nezastomig for Metastatic Castration-Resistant Prostate Cancer in Adult Participants

Key Inclusion Criteria:

1. Is male with histologically or cytologically confirmed adenocarcinoma of the prostate without pure small cell carcinoma
2. Has metastatic castration-resistant prostate cancer with prostate-specific antigen value as described in the protocol and that has progressed within 6 months prior to screening
3. Has received ≥2 lines of prior systemic therapy approved in the metastatic and/or castration-resistant setting (in addition to androgen deprivation therapy) including at least one androgen receptor pathway inhibitor (eg, abiraterone, enzalutamide, apalutamide, or darolutamide)
4. Has had either orchiectomy or be on luteinizing hormone-releasing hormone (LHRH) agonist or antagonist therapy with serum testosterone levels as described in the protocol and agree to stay on LHRH agonist or antagonist therapy during the trial
5. Is able and willing to provide tumor tissue, either archival or newly obtained
6. Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
7. Has adequate organ, bone marrow, renal and hepatic function

Key Exclusion Criteria:

1. Has not recovered (ie, grade ≤1 or baseline) from immune-mediated adverse event within 3 months prior to initiation of trial intervention therapy except for endocrinopathies adequately managed with hormone replacement
2. Has permanently discontinued anti-cancer immune modulating therapies due to immune-mediated adverse events
3. Has another malignancy that is progressing or requires active treatment, except non-melanoma skin cancer that has undergone potentially curative therapy or any tumor that has been deemed to be effectively treated with definitive local control
4. Has ongoing or recent (within 5 years) evidence of significant autoimmune disease (including any history of systemic vasculitis) that required treatment with systemic immunosuppressive treatments
5. Has active liver metastases
6. Has current evidence of or history of central nervous system metastases as described in the protocol
7. Has encephalitis, meningitis, neurodegenerative disease (with the exception of mild dementia that does not interfere with activities of daily living), or uncontrolled seizures in the year prior to first dose of trial intervention
8. Has a known history of, or any evidence of, interstitial lung disease or active, noninfectious pneumonitis (past 5 years). A history of radiation pneumonitis in the radiation field is permitted
9. Has active or recent infection requiring hospitalization or treatment with intravenous anti-infectives within 2 weeks of first dose of trial intervention
10. Has significant cardiovascular disease

Note: Other protocol defined Inclusion/ Exclusion criteria apply