MRC1 and neoplasm: Identification, at the tumor level, of an MMR protein-deficient status/high MSI should be followed by MMR gene testing (which is the gold standard for LS diagnostics); however, this assessment may not always identify a germline mutation; on the other hand, 10% of LS-related MMR germline mutations are not associated with anomalies in MMR proteins at the IHC level [2,4,5,6,7,8,9,10].