KEYNOTE-991: pembrolizumab plus enzalutamide and androgen deprivation for metastatic hormone-sensitive prostate cancer.

Current treatment for patients with metastatic hormone-sensitive prostate cancer (mHSPC) delays disease progression and improves survival, but resistance is inevitable. Additional therapies that prolong survival are needed. Androgen deprivation therapy (ADT) combined with next-generation hormonal agents, such as enzalutamide, is standard-of-care for men with mHSPC. Emerging evidence suggests potential synergism between enzalutamide and the PD-1 inhibitor pembrolizumab in prostate cancer. The phase III randomized, placebo-controlled, double-blind KEYNOTE-991 trial will investigate the efficacy and safety of pembrolizumab versus placebo in combination with enzalutamide when initiating ADT in participants with mHSPC naive to next-generation hormonal agents. Approximately 1232 patients will be randomly assigned 1:1 to receive pembrolizumab 200 mg every 3 weeks or placebo every 3 weeks, both with enzalutamide 160 mg once daily and ADT. Dual primary end points are overall survival and radiographic progression-free survival. Secondary end points include time to first subsequent therapy, time to symptomatic skeletal related event, objective response rate and safety and tolerability. Clinical Trial Registration: NCT04191096 (ClinicalTrials.gov).