Merck to stop Phase 3 KEYNOTE-991 trial

Merck announced that it will stop the Phase 3 KEYNOTE-991 trial investigating KEYTRUDA, Merck’s anti-PD-1 therapy, in combination with enzalutamide and androgen deprivation therapy for the treatment of patients with metastatic hormone-sensitive prostate cancer. Merck is discontinuing the study based on the recommendation of an independent Data Monitoring Committee which reviewed data from a planned interim analysis. At the interim analysis, KEYTRUDA in combination with enzalutamide and ADT did not demonstrate an improvement in overall survival or radiographic progression-free survival, the trial’s dual primary endpoints, compared to placebo plus enzalutamide and ADT. The safety profile of KEYTRUDA in this trial was consistent with that observed in previously reported studies. No new safety signals were identified; however, the combination was associated with a higher incidence of Grade 3-5 adverse events and serious adverse events compared to the control arm. Merck is informing study investigators of the decision and advises patients in the study to speak to their physician regarding treatment. Data from this study will be presented at an upcoming medical meeting.