DNA Mismatch Repair Deficiency in Colorectal Adenocarcinoma by a Two-Antibody Immunohistochemical Approach and its Association with Clinicopathological Features among Bangladeshi Patients

Background: Defective DNA Mismatch Repair (dMMR) genes cause dMMR/Microsatellite Instability (MSI)-related Colorectal Cancers (CRC) in humans which are different from Microsatellite Stable (MSS) tumors in terms of biological behavior, therapeutic response, and prognosis. We aimed to determine the frequency of dMMR CRCs by a two-antibody (PMS2 and MSH6) immunohistochemical approach and to evaluate their association with clinicopathological parameters to document the ever first report of such cases in Bangladesh. Methods: Fifty histopathologically confirmed resected bowel specimens of CRC were studied over a period of two years at a tertiary-level hospital in Bangladesh. Histopathological parameters like morphologic variants, histologic subtypes, grade, stage, Lymphovascular Invasion (LVI), intratumoral lymphocytic infiltrate, and Crohn-like peritumoral reaction were assessed. Immunohistochemistry using PMS2 and MSH6 was performed on representative paraffin blocks by DAKO EnVision method. Expression of both of the markers was evaluated in classified groups. Results: Mean age of study population was 48.60±14.6 years with a male to female ratio of 1.8:1. dMMR was recorded in 32% of cases. Expression of PMS2 and MSH6 were lost in 20% and 12% of cases, respectively. dMMR status was significantly associated with mucinous histology (p=0.014), lower pN staging (p=0.042), low LVI (p=0.002), exhibited intra-tumoral lymphocytosis (p=0.001), and Crohn like peritumoral reaction (p=0.001). No significant association with gender, age, right-sided location, histologic type, pT stage or grade was observed. Conclusion: Frequency of dMMR CRCs was comparatively higher in the Bangladeshi population than in other races. Identification of dMMR tumors by their protein expression pattern using at least two, preferably four antibodies is proposed for routine screening of CRC cases.