2241 - KEYNOTE-641: Phase 3 Study of Pembrolizumab (pembro) Plus Enzalutamide for Metastatic Castration-Resistant Prostate Cancer (mCRPC)

Background

Treatment options for patients (pts) with mCRPC are noncurative, and life expectancy is only about 3 y. Enzalutamide plus the programmed death 1 (PD-1) inhibitor pembro showed activity in abiraterone-pretreated pts with mCRPC in the phase 1b/2 KEYNOTE-365 (NCT02861573) study. In another study (NCT02312557) some pts had profound anticancer response to pembro plus enzalutamide that lasted years. KEYNOTE-641 (NCT03834493) is a randomized phase 3 trial to evaluate efficacy and safety of pembro plus enzalutamide vs placebo plus enzalutamide for pts with mCRPC.

Trial design

Adults (≥18 y) with histologically or cytologically confirmed prostate cancer and mCRPC with biochemical or radiographic progression are eligible. Pts who received chemotherapy for mCRPC, checkpoint inhibition, or any treatment with a second-generation androgen receptor inhibitor (eg, enzalutamide, apalutamide, or darolutamide) are excluded. Pts intolerant to or progressed on prior abiraterone therapy were included. Pts must have ECOG PS 0/1, adequate organ function, and tissue for biomarker analysis. Approximately 1200 pts will be randomly assigned 1:1 to receive enzalutamide 160 mg/d plus pembro 200 mg Q3W or enzalutamide 160 mg/d plus placebo. Treatment will be stratified per prior abiraterone treatment (yes/no), metastases (bone only/liver/other), and prior docetaxel treatment for metastatic hormone-sensitive prostate cancer (yes/no). Responses will be assessed by CT/MRI and radionuclide bone imaging per PCWG-modified RECIST v1.1 every 9 wk during the first year and every 12 wk thereafter. Treatment will continue with enzalutamide plus pembro/placebo until radiographic disease progression, unacceptable toxicity, or consent withdrawal, with a maximum of 2 yr of treatment for the pembro/placebo component of the combination. Primary end points: overall survival and radiographic progression-free survival by blinded independent central review. Key secondary efficacy end point is time to subsequent anticancer therapy or death; safety and tolerability will also be reported.

Clinical trial identification

NCT03834493; February 8, 2019.

Editorial acknowledgement

Medical writing and/or editorial assistance was provided by Matthew Grzywacz, PhD, of the ApotheCom pembrolizumab team (Yardley, PA, USA). This assistance was funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA.

Legal entity responsible for the study

Merck Sharp & Dohme Corp, a subsidiary of Merck & Co, Inc, Kenilworth, NJ, USA.

Funding

Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA. Astellas is providing enzalutamide for this study.

Disclosure

J.N. Graff: Speaker Bureau / Expert testimony: CME activity for i3 Health; Research grant / Funding (institution), Travel / Accommodation / Expenses: Merck; Research grant / Funding (institution), Travel / Accommodation / Expenses: Sanofi; Research grant / Funding (institution): Janssen; Research grant / Funding (institution): Bristol-Myers Squibb. J. Burgents: Full / Part-time employment: Merck; Full / Part-time employment: AstraZeneca; Full / Part-time employment: Array BioPharma; Full / Part-time employment: Merrimack. L.W. Liang: Shareholder / Stockholder / Stock options, Full / Part-time employment: MSD. A. Stenzl: Advisory / Consultancy: Ipsen Pharma, Sanofi Aventis, CureVac, Astellas; Research grant / Funding (institution): Johnson&Johnson, Roche, Cepheid, Amgen Inc, Bayer AG, CureVac, Immatics Biotechnology GmbH, GemeDX Biosciences, Immatics Biotechnologies GmbH, Novartis AG, Karl Storz AG; Speaker Bureau / Expert testimony: GBA; Non-remunerated activity/ies, Patents, but no royalties: No company.