MLH1 and colorectal carcinoma: However, high-frequency MSI occurs in approximately 15% of sporadic colorectal cancers (CRC) and other tumors (Peltomki, 2001), wherein the mismatch repair genes (MMR) defect develops because of epigenetic inactivation of the MLH1 gene by DNA methylation (Cunningham et al., 1998; Poynter et al., 2008; Sinicrope et al., 2010).