The main purpose of this study is to determine the safety, tolerability (how the body reacts to the drug\[s\]) and effectiveness (ability to treat the cancer) of REGN5678 (Nezastomig) alone, or in combination with cemiplimab.
The study has 2 parts. The goal of Part 1 (dose escalation) is to determine a safe dose(s) of REGN5678 when it is given alone or in combination with cemiplimab. The goal of Part 2 (dose expansion) is to use the REGN5678 drug dose(s) found in Part 1 to see how well REGN5678 alone or in combination with cemiplimab works to shrink tumors.
This study is looking at several other research questions, including:
1. Side effects that may be experienced by taking REGN5678 alone or in combination with cemiplimab 2. How REGN5678 alone or in combination with cemiplimab works in the body 3. How much REGN5678 and/or cemiplimab are present in the blood 4. To see if REGN5678 alone or in combination with cemiplimab works to reduce the size of the tumor by helping the immune system destroy the tumor
Men with histologically or cytologically confirmed adenocarcinoma of the prostate without pure small cell carcinoma.
PSA value at screening ≥4 ng/mL that has progressed within 6 months prior to screening as defined in the protocol.
one second-generation anti-androgen therapy (eg, abiraterone, enzalutamide, apalutamide, or darolutamide)
177Lu-PSMA-617 radiotherapy, or another lutetium-based PSMA targeted radioligand, as described in the protocol
Has received treatment with an approved systemic therapy within 3 weeks of dosing or has not yet recovered (ie, grade ≤1 or baseline) from any acute toxicities, as described in the protocol
Has received any previous systemic biologic therapy within 5 half-lives of first dose of study therapy, as described in the protocol
Has received prior PSMA-targeting therapy with the exception of a PSMA targeting radioligand (eg. 177Lu-PSMA-617) in mCRPC
Dose Escalation: Has had prior anti-cancer immunotherapy (other than sipuleucel-T) within 5 half-lives prior to study therapy.