Familial Adenomatous Polyposis (FAP)

Overview

Familial adenomatous polyposis (FAP) is an inherited condition in which numerous growths called polyps develop in the lining of the colon and rectum, often beginning in the teenage years. People with classic FAP typically develop hundreds to thousands of these polyps over time.

Although the polyps themselves start as noncancerous, having so many of them makes it nearly certain that one or more will become colon cancer if the condition is not treated. Because of this very high risk, FAP is managed proactively with regular screening and, in most cases, surgery to remove the colon before cancer develops. A milder form, sometimes called attenuated FAP, involves fewer polyps and later onset. FAP can also affect other parts of the body.

Symptoms

Early on, polyps usually cause no symptoms, which is why screening is so important in affected families. As polyps grow or increase in number, symptoms can include:

• Blood in the stool or rectal bleeding.
• Changes in bowel habits, such as diarrhea.
• Abdominal discomfort.
• Unexplained anemia or fatigue from ongoing blood loss.
• Weight loss in more advanced cases.

FAP can also cause features outside the intestine, such as bumps on bones, certain skin and soft-tissue growths, dental abnormalities, and changes in the back of the eye, though these are not always present.

Causes

FAP is caused by an inherited change (mutation) in a gene called APC, which normally helps control how cells in the colon lining grow. Key points include:

• A faulty APC gene allows cells to grow in an unregulated way, leading to many polyps.
• It is usually inherited in an autosomal dominant pattern, meaning a single changed copy of the gene, inherited from one affected parent, is enough to cause the condition. Each child of an affected parent has a chance of inheriting it.
• In some people, the gene change arises newly without a family history.

Risk Factors

The main risk factor is family history. Risk is higher when:

• A parent or close relative has FAP or a known APC gene change.
• There is a family history of many colon polyps or early colon cancer.

Anyone with a first-degree relative who has FAP should discuss genetic counseling and early screening with their doctor, often beginning in the early teenage years.

Diagnosis

FAP is diagnosed through examination of the colon and genetic testing:

• Colonoscopy or flexible sigmoidoscopy, which can reveal the many polyps that characterize the condition.
• Genetic testing for a change in the APC gene, which can confirm the diagnosis and is used to test at-risk relatives.
• Family history review and, in known families, screening starting in the early teens.
• Examination for features outside the colon, such as eye, bone, and dental findings, in some cases.

When a gene change is known in a family, relatives can be tested to find out whether they are affected and need close screening.

Treatment

Because the risk of colon cancer is so high, treatment focuses on prevention through close monitoring and surgery:

• Regular colonoscopy to monitor polyps, often starting in the early teenage years for those at risk.
• Surgery to remove the colon (and sometimes the rectum), usually recommended once polyps become too numerous to remove individually, to prevent cancer. Different surgical options preserve bowel function in various ways.
• Ongoing surveillance after surgery of any remaining rectum, as well as screening of the upper digestive tract, since polyps can form there too.
• Monitoring and treatment of features outside the colon as needed.
• Genetic counseling for the person and family.

With proactive care, colon cancer can usually be prevented or caught early.

Prevention

FAP itself is inherited and cannot be prevented, but its most serious complication, colon cancer, can often be prevented through:

• Genetic counseling and testing for at-risk family members.
• Early and regular colonoscopy screening, typically starting in the early teens for those who carry or may carry the gene change.
• Timely surgery to remove the colon when recommended.
• Continued surveillance of any remaining bowel and the upper digestive tract.

When to See a Doctor

See a doctor if you have a family history of FAP, many colon polyps, or early colon cancer, so you can discuss genetic counseling and an early screening plan. Children and teens in affected families often begin screening in the early teenage years.

Seek prompt care for rectal bleeding, persistent changes in bowel habits, unexplained anemia or fatigue, or abdominal pain. While these symptoms have many causes, in someone with FAP they should be evaluated quickly.

Related Topics

Frequently Asked Questions

References

1. National Cancer Institute (NCI).
2. American Cancer Society.
3. MedlinePlus, U.S. National Library of Medicine.
4. Mayo Clinic.