We assessed hot spot analysis and immunofluorescence staining in tumor biopsy sections from MSS colorectal cancer patients who were genotyped for lack of mutations in Mlh1, Msh2, Msh6, and Pms2. In consistent with the results observed in the orthotopic CT26-FL3 tumor model, more hot spots were observed in the colorectal tumors from patients endured 2–3 courses of XELOX (capecitabine plus OxP) treatment, compared to those from patients without any treatment (Fig. 7a, b). This evidence concerns the gene MSH2 and colorectal cancer.