Definition of Hereditary nonpolyposis colon cancer

Hereditary nonpolyposis colon cancer: (HNPCC) An hereditary cancer syndrome which carries a very high risk of colon cancer and an above-normal risk of other cancers (uterus, ovary, stomach, small intestine, biliary system, urinary tract, brain, and skin).

The HNPCC syndrome is due to mutation in a gene in the DNA mismatch repair system, usually the MLH1 or MSH2 gene or less often the MSH6 or PMS2 genes. Families with HNPCC account for about 5% of all cases of colon cancer and typically have the following features (called the Amsterdam clinical criteria):

• Three or more family members with colorectal cancer;
• Affected family members in two or more generations; and
• At least one person with colon cancer diagnosed before the age of 50.

The highest risk with HNPCC is for colon cancer. A person with HNPCC has about an 80% lifetime risk of colon cancer. Two-thirds of these tumors occur in the proximal colon. Women with HNPCC have a 20-60% lifetime risk of endometrial cancer. In HNPCC, the gastric cancer is usually intestinal-type adenocarcinoma. The ovarian cancer in HNPCC may be diagnosed before age 40. Other HNPCC-related cancers have characteristic features: the urinary tract cancers are transitional carcinoma of the ureter and renal pelvis; the small bowel cancer is most common in the duodenum and jejunum; and the most common type of brain tumor is glioblastoma.

The diagnosis of HNPCC may be made on the basis of the Amsterdam clinical criteria (listed above) or on the basis of molecular genetic testing for mutations in a mismatch repair gene (MLH1, MSH2, MSH6 or PMS2). Mutations in MLH1 and MSH2 account for 90% of HNPCC. Mutations in MSH6 and PMS2 account for the rest.

HNPCC is inherited in an autosomal dominant manner. Each child of an individual with HNPCC has a 50% chance of inheriting the mutation. Most people diagnosed with HNPCC have inherited the condition from a parent. However, not all individuals with an HNPCC gene mutation have a parent who had cancer. Prenatal diagnosis for pregnancies at increased risk for HNPCC is possible.

HNPCC is also known as the Lynch syndrome after Dr. Henry Lynch at Creighton University in Omaha, Nebraska. HNPCC includes the Muir-Torre Syndrome and Turcot Syndrome.