Colon cancer, a malignant tumor of the large intestine, affects both men and women. It affects 2-6% of all men and women in their lifetime.
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 chance of developing colon cancer is significantly higher than in the average person. Identifying those individuals and families that might be at-risk for hereditary colon and associated cancers can dramatically reduce the number of cancer diagnoses in these families.
Colon Cancer Genes
Several genes have been identified which contribute to a susceptibility to colon cancer. The two most common inherited colon cancer conditions include FAP and HNPCC.
- FAP (familial adenomatous polyposis)
Individuals with this syndrome develop many polyps in their colon (often over 100). People who inherit mutations in the APC gene have a nearly 100 percent chance of developing colon cancer by age 40. In addition, having FAP increases the risk of developing hepatoblastoma, dermoids, fibromas, and other cancers. If a patient has more than 10 adenomatous polyps in their lifetime a cancer risk assessment is appropriate.
- HNPCC (hereditary nonpolyposis colorectal cancer)Individuals with an HNPCC gene mutation have an estimated 80 percent lifetime risk of developing colon or rectal cancer. There is also a 40-60 percent chance for endometrial cancer. Other cancer risks are increased as well.
Patients with the following characteristics should be referred for a cancer risk assessment:
- Patient diagnosed with colon cancer younger than age 50 years.
- Patient has multiple colon cancers or more than one HNPCC related cancer.*
- Patient has colon cancer and one relative with an HNPCC related tumor* under age 50 years.
- Patient has colon cancer and two or more first or second degree (parents, siblings, aunts, uncles, grandparents) relatives with HNPCC related* cancers at any age.
*Colon, endometrial, ovarian, stomach, small bowel, biliary tract or transitional cell of the renal pelvis.