Besides Familial Adenoma Polyposis, there is a colorectal cancer without digestive tract polyposis in which hereditary and family cluster are recognized. This has recognized by clinicians gradually for a long time, and is called cancer family syndrome. Recently, global interests are increased in this colorectal cancer, and it is considered as a name of these symptoms, hereditary nonpolyposis colorectal cancer (HNPCC) is preferable to be referred, and it is inappropriate to refer to "cancer family syndrome" in the international conference held in Amsterdam. HNPCC inherits abnormal dominant inheritance, and as compared to common colorectal cancers,
1. The age of onset of colorectal cancer is young.
2. Most patients are 40years old or under.
3. The incidence of multiple colorectal cancers is high.
4. The incidence of double cancer with the organ other than colon is high.
5. The cancer incidence rate in the right-sided colon (appendix, ascending colon, transverse colon) is high.
Characteristics are as described above.