If MLH1, MSH2, MSH6 and PMS2 mutations cause dMMR, they can be obtained from tumors. Pembrolizumab is FDA approved for dMMR. For patients with body tumors, Nivolumab monotherapy plus Ipilimumab was used for standardization. Patients with dMMR metastatic colorectal cancer after treatment progression can benefit. The gene discussed is MLH1; the disease is metastatic colorectal cancer.