Correlation between mismatch-repair protein expression and clinicopathologic features in 658 colorectal cancers

Abstract

Objective: To investigate the expression of mismatch repair (MMR) proteins (MLH1, MSH2, MSH6 and PMS2) in colorectal cancers and to explore the relationship between MMR expression and clinicopathologic features. Methods: Six hundred and fifty-eight colon cancers were collected from January 2016 to January 2017 at Shengjing Hospital of China Medical University. Of the 658 patients there were 409 male and 249 female. The patients were 20 to 92 years old, with average age of (63±5) years old. Expression of MLH1, MSH2, MSH6 and PMS2 protein was detected by immunohistochemical method. Immunohistochemistry for BRAF V600E was performed in colorectal cancers with loss of MLH1 protein expression. Relationship between MMR protein expression and clinicopathologic features was analyzed statistically. Results: Forty-four cases of 658 cases (6.7%) lost at least one MMR protein expression. Expression deficiency rates of MLH1, MSH2, MSH6 and PMS2 were 4.1%(27/658), 2.3%(15/658), 2.4% (16/658), and 4.3% (28/658), respectively. MMR expression deficiency mainly consisted of combined loss of MLH1/PMS2 (61.4%, 27/44) and MSH2/MSH6 (34.1%, 15/44). Two unique mutations were identified including one MSH6-deficient(2.3%, 1/44) and PMS2-deficient(2.3%, 1/44). Seven cases (25.9%, 7/27) had positive BRAF V600E expression, suggesting BRAF gene mutation related sporadic colorectal cancers. No correlation was observed between the expression of MMR and depth of tumor infiltration, lymph node metastasis, vascular tumor emboli, clinical stage or hematogenous metastasis (P>0.05). MMR status was associated with tumor cell differentiation, histological type and tumor location (P<0.01). Tumors with combined MLH1 and PMS2 loss were associated with mucinous differentiation (P=0.049, P=0.013) and located in the right hemi-colon (P=0.006, P=0.002). Combined MSH2 and PMS2 loss was related to gender, while loss of MSH2 protein was observed more frequently in female patients (P=0.048) and loss of PMS2 protein was seen more frequently in male patients (P=0.031). Conclusions: Patients with MMR protein deficiency have a younger onset age and poorly differentiated tumors. Most tumors are located in the right hemi-colon and have mucinous differentiation.