3071Background: Mismatch repair deficient cancers harbor high levels of microsatellite instability and somatic mutations. Treatment with anti-PD-1 antibodies has resulted in durable objective responses in MSI-H cancer. As part of the ongoing, global, multicenter phase 2 studies KEYNOTE(KN)164 and KN158, we assessed the efficacy of pembrolizumab in patients (pts) with MSI-H tumors. Methods: Both studies enrolled pts with MSI-H status determined locally by IHC or PCR. KN164 enrolled pts with MSI-H CRC and ≥2 prior therapies, whereas the multicohortKN158 study included pts with MSI-H non-CRC and ≥1 prior therapy. Eligible pts in both studies received pembrolizumab 200 mg Q3W until progression, unacceptable toxicity, or pt/investigator decision. Tumor response was assessed every 9 wk by independent review per RECIST v1.1. Primary endpoint was ORR. Secondary endpoints included DOR, PFS, OS, and safety. Analyses were performed in pts from KN164 and KN158 who had ≥27 wk of follow-up as of Aug 3, 2016 and Oct 19,...