Hereditary Colorectal Cancer

Colon cancer, a malignant tumor of the large intestine, affects both men and women. It affects 2 percent to 6 percent of all men and women in their lifetime.  It is the third most commonly diagnosed cancer in both sexes.

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.

Several genes have been identified that contribute to a susceptibility to colon cancer. The two most common inherited colon cancer conditions are FAP (familial adenomatous polyposis) and HNPCC (hereditary nonpolyposis colorectal cancer), now referred to as Lynch syndrome.

  • 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.
  • Lynch syndrome (HNPCC): Individuals with an HNPCC gene mutation have an estimated 80 percent lifetime risk of developing colon or rectal cancer. There is also a 40 percent to 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:

  • Diagnosed with colon cancer younger than age 50 years
  • Multiple colon cancers or more than one HNPCC-related cancer*
  • Colon cancer and one relative with an HNPCC-related tumor* under age 50 years
  • 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.

Gene testing can identify some individuals who carry genes for FAP and some HNPCC cases of colon cancer.

However, the tests are not perfect at this point in time. So, some families may have alterations in the FAP or HNPCC gene that cannot be detected. Although FAP and HNPCC are the most common hereditary causes of colon cancer, there are several additional genes that may also contribute to a family history of colorectal cancer or polyps. Testing for these genes recently became available.

FAP can be a childhood onset condition. Screening for polyps begins between ages 7-12. Some physicians even recommend screening for liver tumors starting at birth. Therefore genetic risk assessment is sometimes done in childhood.

Patients with Lynch syndrome or strongly suspected Lynch need to have colonoscopy exams starting at age 20-25, and this needs to be repeated every one to two years. Also, screening for endometrial cancer is recommended and includes transvaginal ultrasound and endometrial biopsy. This is usually initiated between the ages of 25-35 and repeated every year.

Some patients pursue surgery to reduce their cancer risks. Careful screening can increase early detection of subsequent cancers. These cancers usually start young so screening must start before age 50. Although some of these options may reduce the risk for developing colon cancer, no option totally eliminates this risk.

Additional Information

The National Cancer Institute (NCI) provides additional information on the genetics of colon cancer

Last Updated 10/2016

Who Treats This

Who treats this?
Our Hereditary Cancer Program provides cancer risk-assessment services for children and adults. Our experienced team can evaluate your family history and choose appropriate genetic testing options to determine your child’s risk for familial and hereditary cancers. Learn More