Three patients with mutations in the MMR genes were treated with PD‐1 inhibitors: (1) one patients with unresectable cholangiocarcinoma who had an MLH1 mutation had a near‐complete and persistent response to pembrolizumab (discussed below), and (2) another heavily pretreated patient's metastatic CRC tumor had an MSH6 mutation and another patient's metastatic well‐differentiated high‐grade pancreatic neuroendocrine tumor harbored an MSH2 mutation (this patient's microsatellite status could not be confirmed by IHC). The gene discussed is MRC1; the disease is pancreatic neuroendocrine tumor.