Abstract
Hereditary nonpolyposis colorectal cancer （HNPCC） is an autosomal dominantly in herited disorder showing predisposition to primary cancers from the colorectum, endometrium and other organs. HNPCC is estimated to account for 2 〜5% of all colorectal cancers and one of the most frequent cancer prone syndromes. Disruption of a mismatch repair system is associated with mictosatellite instability（MSI）in tumor tissues and germline mutations of mismatch repair genes such as MSH2 and MLH1 are observed frequently in the HNPCC kindred. As colorectal cancers are not the only one, but many other tumors comprise HNPCC-related tumors, the name “Lynch syndrome” was proposed for cases showing strong evidence of MMR deficiency, e.g., the presence of MMR defect or the presence of MSI in tumors. The name Lynch syndrome is derived from Henry T. Lynch, who discovered the existence of HNPCC or cancer family syndrome in the 1960s.
