Pembrolizumab in men with heavily treated metastatic castration-resistant prostate cancer (mCRPC).

172Background: Pembrolizumabis approved for patients with metastatic, microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) solid tumors who have progressed on prior therapy and have no satisfactory treatment options. However, very few men with PC were included in these initial studies. We evaluated the clinical activity of pembro in a cohort of men with mCRPC and their responses based on molecular genotype. Methods: We performed a retrospective, IRB-approved review of all men with mCRPC in the Duke Cancer Center who were treated with pembro in order to define the duration of therapy, time to PSA-progression, and imaging responsesaccording to prior/concurrent therapy and by molecular subtypes. Results: We identified 51 men who received ≥1 cycle of pembro for mCRPC. Of these, 86% (44/51) had ≥3 prior lines of therapy after ADT, including abiraterone(88%), docetaxel (86%), enzalutamide(enza, 80%), and sipuleucel-T(74%). Somatic tumor sequencing was available in 18/51 men (35%). We...