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NCT03834506 · ClinicalTrials.gov registry record · Phase 3

Study of Pembrolizumab (MK-3475) Plus Docetaxel Versus Placebo Plus Docetaxel in Chemotherapy-naïve Metastatic Castration-resistant Prostate Cancer (mCRPC) (MK-3475-921/KEYNOTE-921)

A Phase 3 study of Prostatic Neoplasms, sponsored by Merck Sharp & Dohme.

Compiled by PlainTrial · August 8, 2026

Completed
Registry status: Phase 3
Development phase: 1,030
Enrollment target: 20
Study locations

NCT03834506: Completed Phase 3 study of Prostatic Neoplasms, sponsored by Merck Sharp & Dohme.

NCT03834506 is a Phase 3 study of Prostatic Neoplasms that has completed, run by Merck Sharp & Dohme. The registered enrollment target is 1,030 participants, above the 498-participant average among 65 other Prostatic Neoplasms trials with a reported enrollment target (107% higher). The trial reports 20 study locations across 15 states. According to ClinicalTrials.gov, the official US trial registry.

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The verdict

NCT03834506, a Phase 3 study of Prostatic Neoplasms, has completed, sponsored by Merck Sharp & Dohme.

COMPLETED
Registry status: Phase 3
Development phase: 1,030 participants
Enrollment target: 20
Study locations

Study Summary

The purpose of this study is to assess the efficacy and safety of the combination of pembrolizumab (MK-3475) and docetaxel in the treatment of men with metastatic castration-resistant prostate cancer (mCRPC) who have not received chemotherapy for mCRPC but have progressed on or are intolerant to Next Generation Hormonal Agent (NHA). There are two primary study hypotheses. Hypothesis 1: The combination of pembrolizumab plus docetaxel plus prednisone is superior to placebo plus docetaxel plus prednisone with respect to Overall Survival (OS). Hypothesis 2: The combination of pembrolizumab plus docetaxel plus prednisone is superior to placebo plus docetaxel plus prednisone with respect to Radiographic Progression-free Survival (rPFS) per Prostate Cancer Working Group (PCWG)-modified Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) as assessed by blinded independent central review.

Primary Outcome

OS was defined as the time from randomization to death due to any cause. The OS was calculated using the product-limit Kaplan-Meier (K-M) method for censored data. Participants without documented death at the time of the analysis were censored at the date of the last follow-up.

Conditions Studied

Prostatic Neoplasms

Interventions

BIOLOGICAL Pembrolizumab
DRUG Placebo
DRUG Docetaxel
DRUG Dexamethasone
DRUG Prednisone

Study Locations (20)

California

St. Joseph Heritage Healthcare ( Site 0069) - Fullerton
University of Southern California Norris Comprehensive Cancer Center ( Site 0061) - Los Angeles
USC Norris Oncology Hematology Newport Beach ( Site 0093) - Newport Beach
University of California San Francisco ( Site 0023) - San Francisco

Michigan

Karmanos Cancer Institute ( Site 0077) - Detroit
Henry Ford Health System ( Site 0039) - Detroit
Cancer & Hematology Centers of Western Michigan ( Site 0013) - Grand Rapids

Alabama

University of South Alabama, Mitchell Cancer Institute ( Site 0065) - Mobile

Colorado

University of Colorado Cancer Center ( Site 0022) - Aurora

Connecticut

Yale Cancer Center ( Site 0038) - New Haven

Florida

Moffitt Cancer Center ( Site 0080) - Tampa

Georgia

Georgia Cancer Center at Augusta University ( Site 0026) - Augusta

Illinois

Mount Sinai Hospital Medical Center ( Site 0042) - Chicago

Trial Details

Field	Value
Enrollment Target	1,030 participants
Start Date	2019-05-02
Est. Completion	2023-07-18
Phase	Phase 3

Merck Sharp & Dohme

558 total trials

What the finished NCT03834506 record still lists

NCT03834506 is an interventional study that assigns participants to a tested intervention. Its 1,030 participants enrollment target places it among the larger protocols in the corpus, above the 498-participant average among 65 other Prostatic Neoplasms trials with a reported enrollment target (107% higher).

The record links to 1 condition, with Prostatic Neoplasms appearing as the primary indexed condition, and to 5 interventions - of which Pembrolizumab is the first listed.

NCT03834506 names 20 study sites across 15 states, led by California, Michigan, Alabama.

Frequently Asked Questions

What is clinical trial NCT03834506 about?

NCT03834506 is a clinical study titled "Study of Pembrolizumab (MK-3475) Plus Docetaxel Versus Placebo Plus Docetaxel in Chemotherapy-naïve Metastatic Castration-resistant Prostate Cancer (mCRPC) (MK-3475-921/KEYNOTE-921)". The purpose of this study is to assess the efficacy and safety of the combination of pembrolizumab (MK-3475) and docetaxel in the treatment of men with metastatic castration-resistant prostate cancer (mCRPC) who have not received chemotherapy for mCRPC but have progressed on or are intolerant to Nex...

What is the current status of trial NCT03834506?

This trial is currently completed. It is a Phase 3 study. The enrollment target is 1,030 participants. The study started on 2019-05-02. Estimated completion is 2023-07-18.

What conditions does trial NCT03834506 study?

This clinical trial studies the following conditions: Prostatic Neoplasms.

What interventions are being tested in trial NCT03834506?

The interventions under investigation include: Pembrolizumab (BIOLOGICAL), Placebo (DRUG), Docetaxel (DRUG), Dexamethasone (DRUG), Prednisone (DRUG).

Who is sponsoring clinical trial NCT03834506?

This trial is sponsored by Merck Sharp & Dohme, which has 558 total clinical trials registered on ClinicalTrials.gov.

Where is trial NCT03834506 being conducted?

This trial has 20 study locations across Alabama, California, Colorado, Connecticut, Florida. Contact the study sites directly through ClinicalTrials.gov for enrollment availability.

Learn More About Clinical Trials

Similar trials for Prostatic Neoplasms

Matched on the same primary condition, ranked to surface studies in the same phase first, then by recruiting status, no relevance scoring or editorial curation.

Where NCT03834506's enrollment target sits among peer trials

1,030 13th of 65 higher than 53 of 65 other Prostatic Neoplasms trials

participants (enrollment target), bucketed by value

Each bar is a band; taller bars hold more other Prostatic Neoplasms trials. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.

Source ClinicalTrials.gov registry export · 2026-08-08

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Source: ClinicalTrials.gov NCT03834506, the US trial registry maintained by the National Library of Medicine. NCT03834506 (large enrollment · wide site footprint · completed) retrieved and formatted by PlainTrial, see methodology.