MSI pathway occurs in approximately 15% of colorectal cancers, and its most common cause is a loss of the DNA mismatch repair function which can result, on the one hand, from germline mutation in an inherited context of Lynch syndrome (also termed: hereditary non polyposis colorectal cancer, HNPCC) or, on the other hand, from epigenetic alterations with hypermethylation of hMLH1 promoter [86,87]. The gene discussed is MLH1; the disease is hereditary nonpolyposis colon cancer.