A form of colon cancer that does not develop from polyps and arises in individuals who have an inherited susceptibility to it. Hereditary nonpolyposis colon cancer (HNPCC) is also known as Lynch syndrome. Individuals who have at least three relatives in two generations who have had colon cancer, with one having had it before age 50, are considered to be at significant risk — two to three times the average risk — for HNPCC. It usually develops at a relatively young age, and women with HNPCC also have an increased risk for developing cancer of the endometrium (lining of the uterus).