Initial Results From A Phase Ii Study Of Nivolumab (Nivo) Plus Ipilimumab (Ipi) For The Treatment Of Metastatic Castration-Resistant Prostate Cancer (Mcrpc; Checkmate 650).

142Background: Immune checkpoint inhibitor monotherapy has shown limited clinical benefit in patients (pts) with prostate cancer, likely due to an immunologically “cold” tumor microenvironment. We report preplanned interim efficacy/safety for NIVO + IPI in pts with mCRPC from CheckMate 650. Methods: Asymptomatic/minimally symptomatic pts who progressed after 2nd-generation hormone therapy and have not received chemotherapy for mCRPC (cohort 1) and pts who progressed after taxane-based chemotherapy (cohort 2) were included. Treatment was NIVO 1 mg/kg + IPI 3 mg/kg Q3W for 4 doses, then NIVO 480 mg every 4 weeks. Coprimary endpoints: objective response rate (ORR) and radiographic PFS per PCWG2. Safety is a secondary endpoint. Exploratory endpoints include correlation of biomarkers with efficacy. Results: 78 pts had a minimum follow-up of 6 months; among pts with baseline measurable disease, ORR was 26% and 10% in cohorts 1 and 2 (Table). In both cohorts, ORR was higher in pts with PD-L1 ≥1%, DNA damage repa...