MSI-H in colon cancer is found in the context of Lynch syndrome, previously known as hereditary non-polyposis colorectal cancer (HNPCC), in which germline mutations in one of four mismatch repair genes (primarily in MLH1 and MSH2 [1] and to a lesser extent in MSH6[2], PMS2 [3] or deletions in EPCAM/TACSTD1 (leading to MSH2 methylation) [4,5] are found. This evidence concerns the gene MLH1 and hereditary nonpolyposis colon cancer.