Lynch Syndrome or Hereditary Nonpolyposis Colorectal Cancer (HNPCC)

Also called Lynch Syndrome, hereditary nonpolyposis colorectal cancer (HNPCC) is the name of a syndrome that predisposes people to develop colon cancer, as well as a number of other cancers. HNPCC is caused by mutations in any of a handful of genes that protect your DNA from accumulating mistakes when cells divide (called "mismatch-repair genes").

The risk for ovarian cancer is increased with hereditary nonpolyposis colon cancer, an autosomal dominant cancer genetic syndrome. A clinical diagnosis of HNPCC is made when all of the following characteristics are present in a family:

• Three or more relatives with colorectal cancer or other HNPCC-related cancer (cancer of the endometrium, ovary, small bowel, ureter, or renal pelvis)
• Cancer affecting at least two successive generations
• One person with cancer is a first-degree relative of the other two
• At least one case of cancer should be diagnosed under the age of 50 years
• A diagnosis of familial adenomatous polyposis (FAP) has been excluded
• The reported history of cancer has been verified by a pathology report

However, some families with mutations in HNPCC-related genes may be tested without demonstrating all of the above characteristics.

These mismatch-repair correct "spelling errors" in DNA that happen during the cell division process. When these genes are altered, or mutated, however, mismatches in the DNA remain which will eventually lead to uncontrolled cell growth and tumor formation.

The risk of developing cancer when you have HNPCC is high. There are a number of rare cancers that HNPCC increases the risk of developing, although the main risks are:

• Colorectal cancers (80%)
• Endometrial cancer (40–60%)
• Gastric cancer (15–20%)
• Ovarian cancer (12%)

HNPCC accounts for about 2–5% of all incidences of colon cancer.