What do we know about heredity and colon cancer?

Colon cancer, a malignant tumor of the large intestine, affects both men and women. In the year 2000, there were an estimated 130,200 cases diagnosed.

The vast majority of colon cancer cases are not hereditary. However, approximately 5 percent of individuals with colon cancer have a hereditary form. In those families, the chances of developing colon cancer is significantly higher than in the average person.

Scientists have discovered several genes contributing to a susceptibility to two types of colon cancer:

• FAP (familial adenomatous polyposis)
  So far, only one FAP gene has been discovered - the APC gene on chromosome 5. But over 300 different mutations of that gene have been identified. Individuals with this syndrome develop many polyps in their colon. People who inherit mutations in this gene have a nearly 100 percent chance of developing colon cancer by age 40.
  
  
• HNPCC (hereditary nonpolyposis colorectal cancer)
  Individuals with an HNPCC gene mutation have an estimated 80 percent lifetime risk of developing colon or rectal cancer. However, these cancers account for only three to five percent of all colorectal cancers. So far, four HNPCC genes have been discovered: