Familial Adenomatous Polyposis (FAP)

Familial adenomatous polyposis (FAP) is an inherited condition that causes many abnormal growths, called polyps, in the gastrointestinal (GI) tract. Polyps increase your risk for colorectal cancer.

Polyps are common in people who do not have FAP, but people with FAP have many more polyps at younger ages than would be expected. People with FAP can develop hundreds or thousands of polyps, where most other people might only have several over their lifetime. These polyps have a very high risk of becoming colorectal cancer over time if they are not removed. People with FAP also have a higher risk of other cancers such as liver, pancreas, thyroid and brain, but these are much less common.

The main types of FAP are:

• Classic FAP: Many people with this type of FAP begin developing colon polyps in their teenage years. Almost all people with classic FAP will have polyps by age 35. Colorectal cancer develops in nearly 100% of people with classic FAP if it is not treated, with an average age of 39 when diagnosed.
• Attenuated FAP: Attenuated FAP is a milder form of FAP. People with attenuated FAP develop fewer colorectal polyps and colorectal cancer later in life than those with classic FAP. Colorectal cancer develops in about 80% of people with attenuated FAP.

Signs and symptoms of familial adenomatous polyposis (FAP)

People with classic FAP can start growing polyps in their colon as early as childhood. Colorectal cancer can develop in these polyps as early as age 20. Early on, colon polyps may not cause any symptoms. As more polyps grow, symptoms can develop. These include:

• Blood in the stool
• Changes in bowel movements, such as diarrhea, constipation, or thin stools
• Trouble having bowel movements when bigger polyps block the intestines, called a gastrointestinal obstruction
• Belly cramps or bloating
• Weight loss not explained by changes in diet or exercise
• Tiredness (fatigue) or low energy
• Anemia (low red blood cells from bleeding polyps)

These symptoms also can be caused by other medical conditions and should be checked by a doctor.

What causes familial adenomatous polyposis (FAP)?

FAP is caused by changes in the APC gene. The APC gene is a tumor suppressor gene. This means the normal APC gene controls growth and division of the cells that make up the gastrointestinal (GI) tract. When the gene is changed, or mutated, this allows unchecked growth of cells in the colon and rectum. This leads to polyps and cancer.

In many cases, the APC gene change is inherited from a parent. But some people with FAP and no family history acquire a new abnormal APC gene. This is called a de novo mutation.

How common is familial adenomatous polyposis (FAP)?

FAP is a rare disease and causes less than 1% of all colorectal cancers.

How is familial adenomatous polyposis (FAP) diagnosed?

FAP may be diagnosed with exams such as a sigmoidoscopy or colonoscopy, and genetic testing (usually a blood test).

FAP may be suspected in people who have or have had:

• Many polyps in the colon and/or rectum (at least 10 to 20)
• A family history of relatives with many polyps in the colon and/or rectum or a known family member with gene changes in APC
• Hepatoblastoma, a cancer of the liver in childhood
• Desmoid tumor (a non-cancerous connective tissue tumor)
• Papillary thyroid cancer
• Unique changes in the retina, a part of the eye, called CHRPE (congenital hypertrophy of the retinal pigment epithelium), especially if it is seen in multiple spots or both eyes

A diagnosis of FAP is confirmed when gene testing shows changes known to cause FAP, called pathogenic mutations, in the APC gene.

If someone in your family has FAP, you might want to ask your doctor about testing. Early testing, before any symptoms, is important and should not be delayed in children of families with FAP.

Does familial adenomatous polyposis (FAP) increase a person’s cancer risk?

Yes, FAP increases a person’s risk for developing several types of cancer. The most common cancer in people with FAP is colorectal, which almost all people with FAP will develop over time if untreated. Other cancers associated with FAP include:

• Cancer of the small intestines
• Stomach cancer
• Thyroid cancer, most often papillary thyroid cancer
• Hepatoblastoma, a liver cancer in children
• Brain cancer, most often medulloblastoma

How is familial adenomatous polyposis (FAP) managed and treated?

There is no cure for FAP, however regular cancer surveillance tests can monitor and remove polyps before they become cancer or catch it earlier when it is easier to treat.

Management of FAP

Colorectal cancer surveillance

People with classic FAP typically begin colorectal cancer surveillance between ages 10 and 15 with a colonoscopy. People with attenuated FAP may start this testing in their later teenage years.

A colonoscopy is a test where a doctor uses a small, flexible tube with a camera on the end to look at the inside of the colon. The tube is placed in the colon through the anus. You will often be given medication to help you relax for the procedure.

During the test, doctors will look at the number, size, and location of the polyps. They may also take biopsies or remove polyps to check for cancer. This test will need to be done regularly to watch for new polyps and cancer.

Upper GI tract cancer surveillance

Surveillance (watching) for cancers of the stomach and small intestine is recommended starting at ages 20 to 25 or when colon polyps are seen, whichever comes first. This is done with a test called an upper endoscopy.

For an upper endoscopy, a doctor uses a small, flexible tube with a camera on the end to look inside the stomach and small intestine. The tube is placed in the stomach through the mouth. You will often be given medication to help you relax for the procedure.

This test will be done every few years to watch for signs of new tumors or cancer. It may be done more often if polyps are detected.

Thyroid cancer surveillance

Regular thyroid ultrasounds may be recommended, starting in a person’s late teen years, to monitor for signs of thyroid cancer.

Hepatoblastoma surveillance

If FAP is diagnosed during infancy, some doctors may recommend surveillance tests for hepatoblastoma, a liver cancer of young children. This may include regular belly exams, abdominal ultrasounds, and alpha-fetoprotein testing (blood tests) every few months for the first several years of life.

Treatment of FAP

Early on, doctors may treat polyps by removing them during a colonoscopy. Over time, many people with FAP develop too many polyps to remove them all during this type of procedure. Because the risk of colon cancer is very high in people with FAP, doctors eventually recommend a surgery to remove the colon, called a colectomy. The timing and exact type of surgery are unique to each person. For example, some people may have a colectomy early before symptoms and others may have surgery when symptoms or cancer develop.

Regular tests to watch for cancer in the rectum or intestines left after surgery will still be needed, but colectomy significantly lowers the chance of colorectal cancer in people with FAP.

Questions to ask your doctor

If you or your family member have FAP, consider asking your doctor:

• What is my risk for developing colorectal cancer?
• What cancer screening tests should I have?
• How many colon polyps have I had?
• What kind of colon polyps have I had?
• What is my risk for developing other cancers?
• What can I do to lower my risk for developing cancer?