What is Hereditary Colorectal Cancer?
Colon cancer is a malignant tumor of the large intestine. It affects 2-6% of all people and is the third most common cancer.
Most colon cancer cases are not hereditary. Only about 5% of people with colon cancer have a hereditary form. In those families, the chance of colon cancer is much higher than for the average person. Identifying people and families that might be at risk for hereditary colon and associated cancers can dramatically reduce the number of cancer diagnoses in these families.
Gastrointestinal (GI) polyposis and cancer in pediatric patients is often due to a hereditary cancer risk syndrome that needs ongoing cancer screening. Figuring out which children are at risk through family history, clinical features of a syndrome, or when symptoms start ensures appropriate cancer risk assessment and management.
Colon Cancer Genes
Several genes that may make a person susceptible to colon cancer have been identified. The two most common inherited colon cancer conditions are FAP (familial adenomatous polyposis) and HNPCC (hereditary nonpolyposis colorectal cancer), called Lynch syndrome.
- FAP (familial adenomatous polyposis)
People with this condition have many polyps in their colon (often over 100). People who inherit changes in the APC gene have a nearly 100% chance of developing colon cancer by age 40. Also, having FAP increases the risk of developing dermoids, fibromas, hepatoblastoma, thyroid cancer, desmoid tumor and medulloblastoma. If a person has more than 10 adenomatous polyps in their lifetime, a cancer risk assessment is appropriate. - Lynch syndrome (HNPCC)
People with an HNPCC gene mutation have about an 80% lifetime risk of developing colon or rectal cancer. There is also a 40-60% chance of endometrial cancer. Other cancer risks are increased as well.
Testing for Colon Cancer
Gene testing can identify some people who carry genes for FAP and some HNPCC cases of colon cancer. But, the tests are not perfect. Some families may have changes in the FAP or HNPCC gene that cannot be detected. Though FAP and HNPCC are the most common hereditary causes of colon cancer, there are other genes that may also contribute to a family history of colorectal cancer or polyps.
Recommendations for Hereditary FAP or HNPCC
FAP can start in childhood. Screening for polyps begins between 7-10 years old. Some doctors suggest screening for liver tumors starting at birth. Genetic risk assessment may be done in childhood.
Patients with Lynch syndrome, or patients with symptoms of Lynch syndrome, need to have colonoscopy exams starting at 20-25 years old. This needs to be repeated every one to two years. Also, screening for endometrial cancer is advised and includes transvaginal ultrasound and endometrial biopsy. This is most often started between 35-40 years old and is done each year.
Some patients have surgery to reduce their cancer risks. Careful screening can increase early detection of cancer later on. These cancers often start young, so screening must start before 50 years old. Some of these options may lower the risk for developing colon cancer, but no option totally gets rid of this risk.
