Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of hereditary colorectal cancer. It is inherited as an autosomal dominant syndrome as a result of defective mismatch repair (MMR) proteins. HNPCC, accounts for 2-5% of all colorectal carcinomas. Over 90% of all colorectal cancers in HNPCC patients demonstrate a high microsatellite instability (MSI-H), which means at least 2 or more genes have been mutated in HNPCC families or atypical HNPCC families.
Colorectal cancer in patients with HNPCC presents at an earlier age than in the general population and is characterized by an increased risk of other cancers, such as endometrial cancer and, to a lesser extent, cancers of the ovary, stomach, small intestine, hepatobiliary tract, pancreas, upper urinary tract, prostrate, brain, and skin.
HNPCC is divided into Lynch syndrome I (familial colon cancer) and Lynch syndrome II (HNPCC associated with other cancers of the gastrointestinal [GI] or reproductive system). The increased cancer risk is due to inherited mutations that degrade the self-repair capability of DNA.
The tumor testing (ie, immunohistochemistry, MSI, germline testing, and BRAF mutation testing), screening, and prophylactic surgery all help to reduce the risk of death in patients with HNPCC or Lynch syndrome.
The benefits of all strategies primarily affect relatives with a mutation associated with HNPCC or Lynch syndrome.
The widespread implementation of colorectal tumor testing helps to identify families with HNPCC or Lynch syndrome.
Colorectal tumor testing could yield substantial benefits at acceptable cost. Particularly in females with a mutation associated with HNPCC or Lynch syndrome who begin regular screening and have reducing surgery. The cost-effectiveness of such testing depends on a particular rate in relatives at risk for HNPCC or Lynch syndrome.