Immunohistochemical Expression of MLH1, PMS2 and P53 in Colorectal Carcinoma with Clinicopathologic Correlation

Background: Proteins of the mismatch repair system and p53 are important for prognosis and treatment of colorectal carcinoma. This raises the need for a better definition of clinical criteria that can be used to detect patients who have defects in these proteins. Objective: To detect the correlations between clinicopathologic features and the expressions of MLH1, PMS2, and p53 in colorectal carcinoma. Methods: This is a cross-sectional analytical study. Tissue samples of 102 colorectal carcinomas were collected in the hospitals of Baghdad Medical City. Archived reports of patients provided clinical and pathological data. The study was done during 2023 and 2024. Immunohistochemical staining results for MLH1, PMS2, and p53 proteins were compared to clinicopathologic criteria and to each other. Results: MLH1 loss was more frequent in tumors of the right colon (p=0.019) and tumors with T3 extension (p=0.05). PMS2 absence was predominant in tumors of moderate differentiation (p=0.04), adenocarcinoma, NOS (p=0.05), tumor-free resection margins (p=0.03), and absence of perineural invasion (p=0.04). The wild expression of p53 was more frequent with the absence of lymphovascular tumor invasion (p=0.04). Aberrant p53 is associated with resection margins clear of tumor invasion (p=0.03), adenocarcinoma, NOS (p=0.05), and grade 2 differentiated tumors (p=0.04). PMS2 is associated with MLH1 (p=0.0001). p53 is associated with PMS2 (p=0.04). Conclusions: A number of CRC clinicopathological variables are related to MLH1, PMS2, and p53 expression status. p53 is correlated with PMS2 status. Consequently, p53 may affect the prognosis of CRC with normal PMS2.