Familial Adenomatous Polyposis (FAP)

Familial adenomatous polyposis (FAP) is an inherited condition. It causes many precancerous growths, called adenomatous polyps, to form in the colon and rectum. Without treatment, at least one of them becomes cancer. This page explains the gene behind FAP, its two main forms, the screening and surgery involved, and what it means for your family.

Reported incidence of FAP varies from about 1 in 7,000 to 1 in 22,000 live births. It accounts for about 0.5% of all cases of colorectal cancer.

FAP is caused by a change in the APC gene. The APC protein helps block a signaling pathway that drives cell growth and division. When APC does not work, that brake is lost, and the lining of the colon grows polyps.

FAP is inherited in an autosomal dominant pattern. That means one changed copy of the gene, from either parent, is enough to cause it. A person with FAP has a 50% chance of passing the APC variant to each child.

In classic FAP, people may have hundreds to thousands of colon polyps.

Polyps start early. The median age at which they appear is 16 years. By age 35, about 95% of people with classic FAP have colon polyps.

Without surgery to remove the colon, colorectal cancer usually develops around age 40. At least 90% of people with classic FAP develop it by age 50.

Those numbers are why prevention in FAP is surgical rather than watchful.

Attenuated FAP (AFAP) is a milder form, but it is not a mild disease.

People with AFAP have fewer polyps, an average of about 30. The polyps are often in the right side of the colon, farther from the rectum.

The lifetime risk of colorectal cancer in AFAP is about 70%. Cancer typically develops around age 55.

The higher position of the polyps matters. A flexible sigmoidoscopy, which only reaches the lower colon, can miss them. Full colonoscopy is needed.

For classic FAP, colonoscopy begins at age 10 to 15 years. For attenuated FAP, it begins in the late teens and is repeated every one to two years. Ask your team how often you need it.

Yes, this means scoping (looking inside with a camera) children. It also means many families face a first colonoscopy conversation during middle school. Ask the genetics team how your center handles that, and whether a pediatric gastroenterologist is involved.

Prophylactic (preventive) surgery to remove the colon improves survival in FAP. The question is not usually whether, but when.

Ask your team which findings would make surgery the next step for you.

Ask which operation is proposed, what happens to bowel function afterward, and whether any rectum is left behind. If rectum remains, it still needs regular endoscopy.

Removing the colon does not end the risk. Polyps also grow in the duodenum, the first part of the small intestine, especially around the ampulla where the bile duct enters.

Duodenal adenomas are found in 80% to 100% of people with FAP. The lifetime risk of duodenal cancer is 4% to 12%.

Upper endoscopy usually starts at age 20 to 25. It may start earlier if relatives had severe duodenal polyps or duodenal cancer. The interval then depends on the Spigelman stage, which grades how bad the duodenal polyps are. NCI's summary lists these NCCN intervals:

• Stage 0 (no polyps): every 3 to 5 years.
• Stage I: every 2 to 3 years.
• Stage II: every 1 to 2 years.
• Stage III: every 6 to 12 months.
• Stage IV: expert surveillance every 3 to 6 months, and a talk about surgery.

Ask for your Spigelman stage by name after each upper endoscopy. It determines when you come back.

Desmoid tumors are growths of fibrous tissue. They are not cancer in the usual sense, because they do not spread to distant organs. But they invade locally, and in the abdomen they can wrap around bowel and blood vessels.

They occur in about 10% to 30% of people with FAP. NCI's summary puts the risk at about 850 times that of the general population.

Report persistent abdominal pain, a firm abdominal lump, or bowel obstruction symptoms to a team that knows FAP.

• Osteomas. Harmless bony growths.
• CHRPE. Congenital hypertrophy of the retinal pigment epithelium, flat pigmented spots on the retina, in up to 80% of people with FAP. An eye exam can find them.
• Thyroid cancer. NCI's summary puts the lifetime risk at about 2%. It notes that NCCN recommends a baseline thyroid ultrasound starting in the late teens. The ultrasound is repeated every 2 to 5 years if normal, and more often with a family history of thyroid cancer. Ask your team how often you need it.
• Hepatoblastoma. A childhood liver cancer. NCI's summary puts the risk at about 850 times the general population's, but the lifetime risk at about 1.6%.
• Brain tumors. About 1% to 2% lifetime risk, mainly medulloblastoma.
• Dental and skin findings. Extra teeth, dental cysts, and skin cysts are common.

Celecoxib and sulindac have been associated with a decrease in polyp size and number. They do not replace surgery or surveillance. NCI notes that the FDA has not approved medicines to manage polyps left in the rectum or pouch after colon surgery. Ask whether either is appropriate for you, and what the cardiovascular and stomach risks are.

Contact your doctor if you have any of these, even between scheduled scopes:

• Blood in the stool, either bright red or very dark.
• A change in bowel habits: diarrhea, constipation, or a feeling that the bowel does not empty completely.
• General abdominal discomfort, such as frequent gas pains, bloating, fullness, or cramps.
• Weight loss for no known reason.
• Fatigue.
• Vomiting.

Go to the emergency department for severe abdominal pain with vomiting and no bowel movement, or for heavy rectal bleeding. Bowel obstruction is a real risk after abdominal surgery and with desmoid tumors.

Every first-degree relative of a person with FAP has a 50% chance of carrying the same APC variant. That includes children, siblings, and parents.

Genetic testing in a family usually starts with the person already affected. Once the exact variant is known, relatives can be tested for that variant.

FAP is one of the syndromes where testing children is appropriate, because colon screening starts at age 10 to 15. Deferring the test does not defer the risk.

• Do I have classic FAP or attenuated FAP, and which APC variant?
• Who owns my colonoscopy schedule, and who owns my upper endoscopy schedule?
• What was my most recent Spigelman stage?
• What is the plan and expected timing for colon surgery?
• Which relatives should be tested, and at what age should children start screening?

• Genetics of Colorectal Cancer (PDQ) Health Professional Version — National Cancer Institute
• Colon Cancer Treatment (PDQ) Patient Version — National Cancer Institute
• Familial Adenomatous Polyposis — MedlinePlus Genetics, National Library of Medicine