The results of MMR protein expression examined by IHC staining showed that among the 131 dMMR/MSI colorectal cancer cases, the double-negative staining of MLH1 and PMS2 was the most common, accounting for 61.07% (80/131), followed by MSH2 and MSH6 double-negative staining, accounting for 16.79% (22/131). The gene discussed is MSH6; the disease is colorectal cancer.