Definition of Hereditary nonpolyposis colon cancer
Hereditary nonpolyposis colon cancer definition - medical term
(HNPCC) An h ereditary 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.
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