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Evaluating the safety and effectiveness of REGN5678 alone or with cemiplimab for advanced prostate and kidney cancer

A Phase 1/2 Study of REGN5678 (Anti-PSMAxCD28) With or Without Cemiplimab (Anti-PD-1) in Patients With Metastatic Castration-Resistant Prostate Cancer and Other Tumors Associated With PSMA Expression

Phase1; Phase2 Interventional Regeneron Pharmaceuticals · NCT03972657

This study is testing if a new drug called REGN5678, alone or with another drug called cemiplimab, can safely shrink tumors in adults with advanced prostate and kidney cancer.

Quick facts

PhasePhase1; Phase2
Study typeInterventional
Enrollment345 (estimated)
Ages18 Years and up
SexAll
SponsorRegeneron Pharmaceuticals Industry-sponsored
Drugs / interventionsipilimumab, immunotherapy, prednisone, cemiplimab
Locations21 sites (Gilbert, Arizona and 20 other locations)
Trial IDNCT03972657 on ClinicalTrials.gov

What this trial studies

This clinical trial aims to assess the safety, tolerability, and effectiveness of REGN5678, both alone and in combination with cemiplimab, in adult participants with metastatic castration-resistant prostate cancer (mCRPC) and clear cell renal cell carcinoma (ccRCC). The study is divided into two parts: the first part focuses on determining safe dosages of REGN5678, while the second part evaluates its effectiveness in shrinking tumors. Researchers will also investigate side effects, how the drug works in the body, and its concentration in the blood.

Who should consider this trial

Good fit: Ideal candidates include men with advanced prostate cancer who have undergone multiple prior therapies or individuals with metastatic clear cell renal cell carcinoma.

Not a fit: Patients with small cell carcinoma of the prostate or those who have not received prior systemic therapy may not benefit from this study.

Why it matters

Potential benefit: If successful, this trial could provide a new treatment option for patients with advanced prostate and kidney cancers.

How similar studies have performed: Other studies have shown promise with similar immunotherapy approaches, suggesting potential for success in this trial.

Eligibility criteria

Show full inclusion / exclusion criteria 
Key Inclusion Criteria:

mCRPC cohorts (men):

1. Men with histologically or cytologically confirmed adenocarcinoma of the prostate without pure small cell carcinoma.
2. PSA value at screening ≥4 ng/mL that has progressed within 6 months prior to screening as defined in the protocol.
3. Has received ≥2 lines prior systemic therapy approved in the metastatic and/or castration-resistant setting (in addition to Androgen Deprivation Therapy \[ADT\]) including at least:

   1. one second-generation anti-androgen therapy (eg, abiraterone, enzalutamide, apalutamide, or darolutamide)
   2. 177Lu-PSMA-617 radiotherapy, or another lutetium-based PSMA targeted radioligand, as described in the protocol

ccRCC cohorts (men and women):

1. Histologically or cytologically confirmed RCC with a clear-cell component.
2. Diagnosis of metastatic ccRCC with at least one measurable lesion via RECIST 1.1 criteria
3. Has progressed on or after ≥1 line prior systemic therapy approved in the metastatic setting. Prior treatment must include an anti-Programmed Death-1 (receptor) \[PD-1\]/Programmed Death-Ligand 1 (PD-L1) therapy and either ipilimumab and/or a tyrosine kinase inhibitor

Key Exclusion Criteria:

1. 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
2. Has received any previous systemic biologic therapy within 5 half-lives of first dose of study therapy, as described in the protocol
3. Has received prior PSMA-targeting therapy with the exception of a PSMA targeting radioligand (eg. 177Lu-PSMA-617) in mCRPC
4. Dose Escalation: Has had prior anti-cancer immunotherapy (other than sipuleucel-T) within 5 half-lives prior to study therapy.
5. Dose Expansion (mCRPC only): Has had prior anti-cancer immunotherapy, as described in the protocol
6. Any condition that requires ongoing/continuous corticosteroid therapy (\>10 mg prednisone/day or anti-inflammatory equivalent) within 1 week prior to the first dose of study therapy
7. Ongoing or recent (within 5 years) evidence of significant autoimmune disease that required treatment with systemic immunosuppressive treatments, as described in the protocol
8. Encephalitis, meningitis, neurodegenerative disease (with the exception of mild dementia that does not interfere with Activities of Daily Living \[ADLs\]) or uncontrolled seizures in the year prior to first dose of study therapy
9. Uncontrolled infection with Human Immunodeficiency Virus (HIV), hepatitis B or hepatitis C infection; or diagnosis of immunodeficiency

NOTE: Other protocol defined Inclusion/Exclusion Criteria apply

Where this trial is running

Gilbert, Arizona and 20 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Metastatic Castration-Resistant Prostate CancerClear Cell Renal Cell Carcinoma
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.