Pts with mCRPC who progressed following ≥1 line of therapy and ImS+ were eligible. ImS+ was defined by ≥1 of the following: 1) mismatch repair deficient (MMRD) by immunohistochemistry (IHC); 2) DNA damage repair deficient (DDRD) excluding MMRD, detected by the UW-OncoPlex targeted exome sequencing assay...The overall CRR was 9/35 (26%, 95%CI 12-43%).... NIVO + IPI demonstrated significant activity in biomarker selected, pre-treated pts with mCRPC.