A Phase 3, Randomized, Double-blind Trial of Pembrolizumab (MK-3475) Plus Enzalutamide Versus Placebo Plus Enzalutamide in Participants With Metastatic Castration-Resistant Prostate Cancer (mCRPC) (KEYNOTE-641)

Principal Investigator

Tom Beer

Study Purpose

The purpose of this study is to test the safety, tolerability, effectiveness of the study drug called pembrolizumab (MK-3475), and to compare any good and bad effects of using the study drug along with enzalutamide compared to using placebo with enzalutamide. Pembrolizumab has been approved by the FDA, is available by prescription to treat several different cancers, but has not been approved to treat prostate cancer.

Medical Condition(s)

Metastatic prostate cancer by image studies
Chemotherapy-naïve metastatic castration resistant prostate cancer
Pembrolizumab versus placebo plus enzalutamide

Eligibility Criteria

- Metastatic prostate cancer patient who may previously be treated with next-generation AR-targeted therapy abiraterone acetate without prior chemotherapy treatment for mCRPC
- Subjects' prostate cancer progressed despite previous androgen deprivation therapy or anti-androgen therapies.
- Subject must supply a newly biopsied tumor tissue or have a tumor tissue previously collected from a previous procedure.
- Subjects have not have an active autoimmune disease that has required systemic treatment in past 2 years.
- Subjects have not have a diagnosis of immunodeficiency or are receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone or equivalent)

Age Range

18 - NA

Healthy Volunteers Needed


Duration of Participation

Up to 24 months

Minors Included



Clinical Trials Information Line: Phone 503-494-1080 or


Merck Sharp & Dohme Corp., (a subsidiary of Merck & Co. Inc.)

Recruitment End


Compensation Provided


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