Germline mutations in mismatch repair (MMR) genes (mostly in MLH1 and MSH2) are associated with hereditary nonpolyposis colorectal cancer (HNPCC), a highly penetrant autosomal-dominant syndrome characterised by several affected individuals with colorectal cancer (CRC) or extracolonic tumours of the endometrium, stomach, small bowel, ureter, renal pelvis, ovary, and hepatobiliary tract (Lynch and de la Chapelle, 2003). This evidence concerns the gene MSH2 and hereditary nonpolyposis colon cancer.