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Patient education: Familial adenomatous polyposis (The Basics)

Patient education: Familial adenomatous polyposis (The Basics)

What is familial adenomatous polyposis? — Familial adenomatous polyposis (called "FAP" here) is a disease that causes abnormal growths in the large intestine (also called the colon), rectum, and other areas (figure 1). Doctors call these growths "polyps." They are not cancer, but can turn into cancer.

Most people with FAP have hundreds or thousands of polyps. This means they have a much higher risk of colon cancer than other people. Without treatment, almost all people who have classic FAP get colon cancer by the age of 39 years. Some people have a milder form of FAP that causes fewer polyps (less than 100). In these people, cancer can develop later in life (in their 50s).

People with FAP can also develop cancer of the stomach, small intestine, thyroid, pancreas, or brain.

FAP is caused by an abnormal gene. This gene often runs in families. But some people have the abnormal gene even though no one else in their family had polyps or cancer. People who have FAP usually start showing signs of it in their teens or 20s. But some people get it in childhood.

What are the symptoms of FAP? — FAP might not cause any symptoms. If it does, symptoms can include:

Bright red blood in bowel movements

Diarrhea – Runny, watery bowel movements.

Constipation – Trouble having bowel movements.

Belly cramps

Weight loss

Bloating – Feeling like the belly is full all the time.


If someone in your family has FAP, you might have regular tests to check for it. Your doctor or nurse might find it before you have symptoms.

Will I need tests? — Yes. Your doctor or nurse will do an exam and learn about any symptoms you have. You might also have the following tests:

A test called a "colonoscopy" – In this test, the doctor puts a tube and a tiny camera through your anus and into your colon (figure 2). During the test, they can check for polyps and take samples of tissue for testing. Another doctor looks at the tissue under a microscope. It can show if you have FAP or a different condition.

A test called a "sigmoidoscopy" – This test is very similar to a colonoscopy, but it only looks at the last part of the colon, close to the rectum.

A test called an "upper endoscopy" – This test uses a tube and tiny camera to check the upper digestive system (figure 3). The doctor can also take samples of tissue in this test.

Genetic testing – This is a blood test to look for the abnormal gene that causes FAP. Before the test, you will talk with a genetic counselor. A genetic counselor is a person who can help you understand what having the gene could mean for you and your family.

You might have these tests in a different order or more than once. For example, if someone in your family has FAP, you might have genetic testing to see if you have the abnormal gene. Or you might have a colonoscopy to look for polyps. If a genetic test shows you have FAP, you might have a colonoscopy or flexible sigmoidoscopy and upper endoscopy. The tests can show your doctor how many polyps you have and where they are.

If you have FAP, your doctor might do exams or tests to look for other types of cancer, such as thyroid cancer.

How is FAP treated? — Treatment depends on your situation. Treatments include:

Surgery to take out the colon – This is called a "colectomy." It is the main treatment for FAP. Taking out the tissue with polyps lowers the risk of cancer.

Polyp removal – Some people have a milder form of FAP that causes fewer polyps. Sometimes, doctors can remove polyps during a colonoscopy or endoscopy instead of doing a colectomy.

Your doctor will talk with you about the treatment most likely to prevent cancer in your situation.

More on this topic

Patient education: Colectomy (The Basics)
Patient education: Colon and rectal cancer screening (The Basics)
Patient education: Colonoscopy (The Basics)

Patient education: Screening for colorectal cancer (Beyond the Basics)
Patient education: Colonoscopy (Beyond the Basics)
Patient education: Colon polyps (Beyond the Basics)

This topic retrieved from UpToDate on: Jan 01, 2023.
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