344 Phase 3 trial of pembrolizumab and enzalutamide versus enzalutamide in patients with metastatic castration-resistant prostate cancer (mCRPC) (KEYNOTE-641)

Background Antitumor activity with pembrolizumab + enzalutamide was observed in cohort C of the phase 1b/2 KEYNOTE-365 (NCT02861573) study of abiraterone acetate–pretreated patients with mCRPC and in a phase 2 study (NCT02312557) of patients with mCRPC who experienced progression with enzalutamide alone. In KEYNOTE-365 cohort C, prostate-specific antigen (PSA) response rate was 22%, objective response rate (ORR) was 20%, and 12-month PFS and OS rates were 24.6% and 72.8%, respectively. Safety and tolerability of the combination was consistent with individual profiles of each agent. In the phase 2 study of enzalutamide-pretreated patients, 5 of 28 patients (18%) had a PSA decline of ≥50%, and 3 of 12 patients (25%) with measurable disease achieved objective response. KEYNOTE-641 (NCT03834493) is a randomized, phase 3 trial to assess efficacy and safety of pembrolizumab + enzalutamide versus placebo + enzalutamide in patients with mCRPC. Methods Enrolled patients have biochemical or radiographic progression with androgen deprivation therapy/after bilateral orchiectomy within 6 months of screening, ECOG PS 0/1, ongoing androgen deprivation with serum testosterone Results N/A Conclusions N/A Trial Registration ClinicalTrials. gov, NCT03834493 Ethics Approval The study and the protocol were approved by the Institutional Review Board or ethics committee at each site.