Hereditary nonpolyposis colon cancer (HNPCC), also known as Lynch syndrome, is a type of inherited cancer of the large intestine. People who have HNPCC are at increased risk for developing small growths of excess tissue (polyps) in the large intestine early in life, making it more likely the growths will become cancerous.

A person with HNPCC may develop colon cancer at an early age (before age 50).

These features are common in families with HNPCC:

• A member of the family has at least three relatives who have had colon cancer, endometrial cancer, or another HNPCC-related cancer, and at least one of the relatives is a parent, brother, or sister.
• Those relatives are spread over two generations in a row (for example, a grandparent and a parent).
• One of those relatives had colorectal or endometrial cancer before age 50.

A genetic test can tell if a person carries the gene for HNPCC.

Experts recommend that people with HNPCC have a colonoscopy every 1 to 2 years starting at age 20 to 25, or 10 years younger than the age at which the youngest family member who has colorectal cancer was diagnosed, whichever comes first.