MLH1, PMS2, MSH2, MSH6 in the pathology report of gastric cancer generally refer to several mismatch repair genes, and the mutation of any one of these genes will lead to the defective function of cell mismatch repair, and as a result, it will produce genetic instability, which is manifested as replication errors or microsatellite instability, and thus is prone to tumor development. Moreover, based on the results, it can also be determined that the patient’s gastric cancer is associated with genetic factors. MLH1, PMS2, MSH2, MSH6 are four common mismatch repair genes. Generally, patients with mutations in these genes are susceptible to a variety of tumors, such as intestinal cancer, gastric cancer, endometrial cancer and so on. Moreover, the presence of mutations in mismatch repair genes also suggests that the occurrence of this cancerous lesion is associated with genetic factors. Gastric cancers with mutations in mismatch repair genes such as MLH1, PMS2, MSH2, MSH6, etc., generally have a young age of onset, are genetically susceptible, and are generally more sensitive to immunotherapy.