MLH1 and hereditary nonpolyposis colon cancer: Around 15–20% of CRCs are MSI-H, mainly due to epigenetic silencing of the hMLH1 gene promoter (Herman et al, 1998), whereas 2–3% of the total of CRCs are due to germ-line mutations in the MMR genes hMLH1, hMSH2, hMSH6, and PMS2, which are the cause of hereditary non-polyposis CRC (HNPCC) cases (Aaltonen et al, 1998; Salovaara et al, 2000).