Immunohistochemical Assessment of MMR Proteins and Morphological Features of Colon Carcinomas

The study aimed to determine the frequency of microsatellite instability (MSI) in colorectal carcinomas, characterize morphological features of dMMR/MSI-H tumors, and assess their diagnostic and prognostic value. A retrospective analysis of 43 colorectal cancer cases was performed. Morphological parameters (mucinous component, medullary type, Crohn-like reaction, TILs, tumor budding) and immunohistochemical expression of MLH1, PMS2, MSH2 and MSH6 were evaluated. The frequency of dMMR was 18,6%. MSI-H tumors were more frequently right-sided, showed low/intermediate differentiation, pronounced TILs and Crohn-like lymphoid reaction. Tumor budding was predominantly Bd1, consistent with a favorable biological profile. The findings support the necessity of routine MMR testing in colorectal cancer diagnostics.