Familial Adenomatous Polyposis: APC Mutations | Genetics and Hereditary Cancers

What You Should Know About Familial Adenomatous Polyposis (FAP)

FAP is a very rare condition that accounts for about 1% of new cases of colorectal cancer. At UT Southwestern, we have one of the largest hereditary cancer programs in the country and are experienced in working with individuals who have FAP.

People with FAP typically develop hundreds to thousands of polyps (adenomas) in their colon and rectum by age 30-40. Polyps may also develop in the stomach and small intestine. People with FAP can develop noncancerous cysts on the skin (epidermoid cysts), especially on the scalp. Besides having an increased risk for colon polyps and cysts, people with FAP are also more likely to develop sebaceous cysts, osteomas (benign bone tumors) of the jaw, impacted teeth, extra teeth, CHRPE (multiple areas of pigmentation in the retina in the eye), and desmoid disease. Some people have a milder form of FAP, called attenuated FAP (AFAP), and develop an average of 20 polyps at a later age.

Cancer Risks Associated with FAP

If left untreated, the polyps in the colon and rectum will develop into cancer, usually before age 50. People with FAP also have an increased risk for stomach cancer, papillary thyroid cancer, periampullary carcinoma, hepatoblastoma (in childhood), and brain tumors.

Managing Cancer Risks

UT Southwestern’s Genetic Cancer Prevention Clinic (GCPC) can help ensure people are receiving appropriate cancer surveillance and management based on their genetic testing results. For more information about the GCPC or to request an appointment, please call us at 214-645-2563.

Gastroenterology specialists work with patients to establish a personalized cancer surveillance plan.
Our specialists follow National Comprehensive Cancer Network (NCCN) recommendations, including:
- Annual colonoscopy
- Surgery to remove the colon once polyposis is detected
- Consideration of nonsteroidal anti-inflammatory drugs (NSAIDS) to reduce the number and progression of polyps
- Upper endoscopy, with frequency dependent on findings
Other Cancers
- UT Southwestern experts in internal medicine, surgical oncology, and other specialties may also be an important part of the care team.
- Additional surveillance or management recommendations may include:
  - Thyroid exam every two to five years
  - Consideration of blood AFP levels and/or abdominal imaging studies for children under age 5
  - Education on the signs and symptoms of other cancers/tumors to prompt imaging

Risks to Family Members

FAP is caused by mutations in the adenomatous polyposis coli (APC) gene. Approximately one-third of people with FAP do not have a family history of the disease and thus have a new mutation. FAP is inherited in a dominant fashion. Children of a person with an APC mutation have a 50% risk of inheriting the mutation. Brothers, sisters, and parents of people with FAP should also be checked to see if they have an APC mutation. Almost everyone who has an APC mutation will develop FAP.