MLH1 and hereditary nonpolyposis colon cancer: In the sporadic form of CRC the most commonly present mutation is an epigenetic alteration, hMLH1 promotor hypermethylation, and its subsequent lower expression.29 MSI-H is an early event in CRC carcinogenesis, it is present in 57% of HNPCC adenomas and in 3% of sporadic adenomas.37