MRC1 and neoplasm: Mismatch repair proteins deficiency (MMRD) can be studied by different methods in tumour tissue, but the most commonly used in the routine practice are immunohistochemistry (IHC) to analyze the expression of MMR proteins (MLH1, PMS2, MSH2 and MSH6) and/or microsatellite instability (MSI) analysis [1, 2].