Expression status of four mismatch repair proteins in patients with colorectal cancer: clinical significance in 1238 cases.

To investigate the expression of mismatch repair proteins (MMR) in colorectal cancer (CRC) and to analyze the correlation between MMR and pathologic features of CRC, immunohistochemistry was used to detect the expression of four MMR proteins (MLHl, PMS2, MSH2 and MSH6). All expression was classified as MMR proficient (pMMR). Absence of one or more of these proteins was classified as MMR deficient (dMMR). Among the 1238 cases of CRC, the four protein expression deletion rates from high to low were: PMS2 5.09% (63/1,238), MLH1 3.47% (43/1,238), MSH6 2.83% (35/1,238), and MSH2 2.10% (26/1,238). The dMMR cases accounted for 8.08% of all CRC cases (100/1,238). The common deletion rates of two or more proteins from high to low were: MLH1/PMS2 41.00% (41/100), MSH2/MSH6 20.00% (20/100), MSH6/PMS 23.00% (3/100), MLH1/MSH2/MSH6/PMS2 1.00% (1/100). dMMR cases were more common than pMMR cases in the ascending colon, T4 stage, stage II group, and poorly-differentiated CRC (P<0.05). MLH1 and PMS2 protein expression deficiency were correlated with tumor site, T stage, and differentiation. The incidence in ileocecum, T4, and poorly differentiated CRC was higher (P<0.05), and these two were positively correlated (P<0.05). The deficiency of MSH2 and MSH6 proteins was correlated with age, tumor site, and TNM stage; it was higher in patients ≤65 years old, in the transverse colon-splenic flexure region, and in stage II CRC (P<0.05), and the two were positively correlated (P<0.05). A co-expression deficiency of MLH1/PMS2 and MSH2/MSH6 was more common. The incidence of dMMR was more common in ascending colon, T4 stage, stage II, and poorly differentiated CRC. This may provide more comparisons and reference data for the molecular mechanism, clinical treatment, and prognosis of CRC.