Expression of Mismatch Repair Proteins in Triple Negative Breast Carcinoma Patients and its Correlation with the Clinicopathological Parameters

Background: Triple negative breast carcinoma (TNBC) is an aggressive disease, with a lack of response to targeted therapies, leaving a limited list of effective treatments, including chemotherapy and radiotherapy. Recent studies have shown that certain types of TNBC are immunogenic tumors, that may be suitable targets for immunotherapies. On the other hand, mismatch repair (MMR) expression status is considered an effective biomarker for assessing susceptibility to immunotherapies in multiple solid tumors.   Objectives: To assess the expression status of the MMR proteins and their correlation with the clinicopathological parameters in TNBC patients. Materials and Methods: Fifty-three formalin-fixed paraffin-embedded histopathological blocks of diagnosed triple negative invasive ductal breast carcinoma cases were retrieved from the archives department of the histopathological laboratories in Medical City campus hospitals. These blocks were sectioned and stained with monoclonal antibodies, targeting four MMR proteins (MSH2, MSH6, MLH1, and PMS2) to assess the expression status of these proteins in the tumor cells. Results: Of 53 cases, there were 10 (18.9%) deficient in the expression of one or more of the MMR proteins, the MSH2 protein was the least frequently missed protein (n = 3, 5.7%). While PMS2 was the most frequently missed one (n = 10, 18.9%). An insignificant correlation (P-value > 0.05) was found between MMR status and the clinicopathological parameters except for age (P-value < 0.05). Conclusion: Deficient expression status of the MMR proteins was common and showed an insignificant relation with the clinicopathological parameters.