MRC1 and cancer: Among three cohorts of patients, including 25 patients with MMR-deficient CRC, MMR-proficient CRC, and MMR-deficient cancers including uterus, stomach, prostate, duodenum, and bile ducts, those patients with MMR-deficient tumors had a response rate to pembrolizumab of approximately 60 %, as compared with 0 % for patients with MMR-proficient tumors.