To confirm the diagnosis of Lynch syndrome: 1. You can first cut several pathological sections (white films) from the pathology department. Immunohistochemistry is done through these pathology sections to clarify the expression of the four genes of Lynch syndrome, MLH1, MSH2, MSH6, PMS2, and then MSI (microsatellite instability); after the initial screening, the genes that are not expressed in MLH1, MSH2, MSH6, PMS2 are further excluded for methylation and BRAF mutations; finally, blood genes are drawn for the genes that are not expressed. Sequencing to check whether there are mutated loci. 2.If you cannot obtain pathological sections of resected tumor tissue, you can directly draw blood for four-gene sequencing, without the initial screening of pathological sections, all four genes may have to be measured, which is relatively more expensive. For stage III colon cancer, it is beneficial regardless of microsatellite instability. For stage II colon cancer, receiving chemotherapy may not have much room for survival improvement because the prognosis of microsatellite unstable stage II colon cancer itself is better.