Overview of Familial Adenomatous Polyposis

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Familial adenomatous polyposis (FAP) is a rare, inherited syndrome that can lead to cancer in the colon, rectum, or other areas of the body. Colon and rectal cancers are often referred to as "colorectal cancer."

FAP can be diagnosed when you have more than 100 benign (noncancerous) growths called polyps or colorectal adenomas. It eventually causes hundreds to thousands of such growths in the colon and rectum.

Familial adenomatous polyposis has an estimated prevalence of 1 in 8,000 to 1 in 18,000 and accounts for less than 1% of all colorectal cancers in the United States.

FAP is responsible for about .5% of the total number of colon cancer cases in general.


FAP is also known as:

  • Adenomatous polyposis of the colon (APC)
  • Familial multiple polyposis
  • Hereditary polyposis coli
  • Multiple polyposis of the colon

Genetics and Timelines

FAP is an autosomal dominant disease. That means someone with the condition has one copy of a mutated gene and one normal copy. They can pass on either one to a child, so each child has a 50% chance of inheriting the gene.

In an affected person, polyps can start forming in the teenage years. If they go untreated, the polyps may become cancerous. The average age for someone with FAP to develop cancer is 39 years old.

Some cases of FAP are classified as "attenuated FAP." In these cases, cancer develops later—at an average of 55 years old—and the number of the polyps is between 10 and 100.

Familial Adenomatous Polyposis
Illustration by JR Bee, Verywell 


It is possible to go a long time having lots of polyps in your colon or rectum without experiencing any symptoms at all. In some cases, the symptoms will eventually show up, and in others, there will be no symptoms until the polyps become cancerous.

Adenomatous Polyps

The polyps in FAP are referred to as "adenomatous." Adenomatous polyps start out as benign but eventually change into being cancerous (malignant). For this reason, they are often referred to as pre-cancerous. These polyps start developing in the person at around 16 years of age.

The polyps usually grow in the colon, but sometimes tumors may develop in other parts of the body, including the:

  • Small intestine (in the duodenum)
  • Central nervous system
  • Abdomen (called desmoid tumors)
  • Eyes
  • Skin
  • Thyroid

When a person has these other types of tumors and osteomas in addition to polyps in the colon, it is sometimes called Gardner's syndrome.

Other Cancers

The presence of tumors in other organs of the body along with FAP comes with an increased risk of developing other types of cancers, such as:

Removal of Colon Polyps

If the polyps are not treated by removing part or all of the colon (a procedure called a colectomy), the development of cancer when a person is in their 30s or early 40s is almost inevitable.

Further Symptoms

More symptoms of FAP include:

  • Other polyps in the stomach and small intestine
  • Osteomas, which are new bones that grow on existing bones
  • Dental malformations (extra or missing teeth)
  • Congenital hypertrophy of the retinal pigment epithelium (CHRPE), or a flat black spot on the retinal pigment epithelium (people with CHRPE have this spot from birth)
  • Rectal bleeding, or basically any blood that passes through the anus (usually in the form of blood in the stool)
  • Unexplained weight loss
  • A change in bowel movement, and in the color or consistency of the bowel movement.
  • Stomach/abdominal pain


Classic and attenuated FAP are caused by mutations in the APC (adenomatous polyposis coli) gene. The APC gene is responsible for the production of the APC protein. This APC protein is, in turn, responsible for controlling how frequently cells divide. Basically, it suppresses cell division so they don't divide too fast or uncontrollably.

When there's a mutation in the APC gene, there tends to be an overgrowth in cells. This is what causes the numerous polyps in FAP to form.

There is another type of FAP called autosomal recessive familial adenomatous polyposis. It is milder and is characterized by fewer than 100 polyps. It's caused by a mutation in the MUTYH gene. When there is a mutation in this gene, errors formed during cell replication (before cell division) are prevented from being corrected. This type of FAP is also called MYH-associated polyposis.

Risk Factors

Having first degree relatives with FAP is the main risk factor for developing the disease. Some people have no family history, however, and the disease is attributed to random gene mutaions.

Screening for people at risk of having FAP usually starts at 10 to 12 years of age. For those believed to be at risk for attenuated FAP, screening usually starts in the teenage years.


Many different tests and procedures are used to diagnose FAP. Those chosen by your healthcare provider will depend on the assessment of your symptoms and other factors such as your family history. Having about 10 to 20 colorectal adenomas, especially in combination with the other symptoms associated with FAP like desmoid tumors, congenital hypertrophy of the retinal pigment epithelium (CHRPE), and polyps in the small intestine, typically leads to an FAP diagnosis.

Colon Examination

A colon exam can be used to definitively diagnose FAP. Usually, a healthcare provider will order this to find out the cause of some of the symptoms that are experienced. Colon examination can be done in many ways.

Methods for Colon Examination

  • Colonoscopy
  • Sigmoidoscopy
  • CT Colonography
  • Barium Enema


This involves using a flexible tube that is fitted with a small camera and a light to look at the whole colon and rectum. Before undergoing this procedure, your healthcare provider will give you special instructions for your diet to follow for up to a few days beforehand. You will also be required to clear out your bowels using laxatives or an enema.

Usually, sedatives are given before the procedure is started. Undergoing this test can cause discomfort and even sometimes pain. However, it is the best way to detect colon polyps as well as colon cancer. If numerous polyps are found in the colon and/or rectum during this test, then a diagnosis of FAP could be made.

The healthcare provider may also take out polyps tissue (biopsy) during the colonoscopy for further testing.


This is very similar to a colonoscopy except that it involves using a short flexible scope to examine only a portion of the colon and rectum. You may also have to clear out your bowels for this procedure, too, but usually not as thoroughly as with a colonoscopy. Sigmoidoscopy is sometimes called flexible sigmoidoscopy.

CT Colonography

This test involves using a CT scan to obtain clear and detailed images of the colon and rectum. The healthcare provider will then be able to identify whether there is the presence of polyps. The bowels must be completely cleaned out and prepped for clear and optimum image quality to be obtained.

During this procedure, carbon dioxide or air is pumped into the colon and rectum, and a CT scanner is used to take pictures of those areas. (Sedatives are not needed for this.) It's also called a CTC, virtual colonoscopy (VC), or CT Pneumocolon.

If numerous polyps are seen, the healthcare provider may make a diagnosis or may order a colonoscopy to confirm the diagnosis of FAP.

Barium Enema

This a type of X-ray of the colon. This method of diagnosis is no longer really used as frequently as the other methods.

Genetic Testing

These are non-invasive ways to diagnose FAP, and they're suitable for those that may not want to undergo invasive procedures like the colonoscopy or the sigmoidoscopy. They are also recommended when a family history of FAP is present.

Blood Test

If your healthcare provider suspects that you have FAP, a special blood test that can detect mutations in the APC and MUTYH genes may be ordered.


Once FAP is diagnosed, it must be treated. Otherwise, it will progress into colorectal cancer. If the polyps are discovered at a very young age, the healthcare provider may try to remove them individually. Eventually, however, there will be too many polyps for this to be effective.


If the polyps are unable to be removed individually, the next course of action is surgery. A variety of different surgeries are available.

Colectomy and Ileorectal Anastomosis

A colectomy involves removing the entirety of the colon but leaving part of the rectum untouched. The part of the rectum that is left will then be surgically connected to the small intestine. This type of surgery preserves bowel function and is usually chosen for people whose polyps are not as numerous.

Colectomy and Ileostomy

In this procedure, your entire colon and rectum are removed. The surgeon will create an opening, usually in the abdomen, where he/she will bring the small intestine through and waste will collect in a bag attached there.

This surgery is sometimes temporary, although in other cases, the bag may remain to collect waste.

Restorative Proctocolectomy

This involves removing the entirety of the colon and most or all of the rectum. The end of the small intestine is then surgically connected to the rectum, and a small pouch called an ileoanal pouch is created there. This way, waste can be stored in this pouch and your bowel function is preserved.

All patients diagnosed with FAP need to eventually undergo one type of colectomy or the other to prevent colon cancer.


Medication is sometimes additionally prescribed to treat FAP. While the aim of surgery is to remove the polyps, surgery does not in itself cure the condition. If you underwent colectomy and ileorectal anastomosis where a significant part of the rectum was left untouched, your healthcare provider may prescribe a drug called Sulindac.

Sulindac is an anti-inflammatory drug that is mostly used to treat arthritis, but it has also been found to be able to shrink polyps in the colorectal area. Thus it can be used to get rid of any remaining polyps after colectomy and prevent them from coming back. This medication has many side effects which should be thoroughly discussed with your healthcare provider before you start taking it.

Sulindac is not yet approved by the FDA in the treatment of FAP. Despite this, it is widely and commonly used.

Another arthritis drug exists called Celecoxib, which is FDA approved. It reduces the number of polyps in the colon and rectum.

It’s important to note that these medications do not necessarily reduce the risk of cancer developing in people with FAP.

Treatment for Other Organs

Many people with FAP also have polyps and tumors in other parts of the body like the stomach, small intestine, and thyroid. These polyps and tumors, especially the ones with the propensity to become cancerous, should be surgically removed.

Other tumors, like the desmoid tumors in the abdomen (which are benign), may not need to be removed if they are not compressing any organs or blood vessels. However, they still need to be monitored.


Surgery doesn’t cure the FAP and polyps may still continue to grow. Having FAP means you’ll have to go for regular medical screenings for the rest of your life.
Depending on your healthcare provider and his/her specific instructions, you may have to undergo:

  • Colonoscopy or sigmoidoscopy every one to three years to check for polyps in the colon and rectum
  • Esophagogastroduodenoscopy every one to three years to check for duodenal tumors or cancer
  • CT scans or MRIs every one to three years to check for desmoid tumors

The purpose of these regular screenings is to check for new polyps and tumors that may develop into cancerous ones if not monitored and subsequently removed.

Your healthcare provider will likely have you undergo the following tests at regular intervals once you've been diagnosed with FAP. They are used to screen for extra-colonic malignancies.

  • Upper endoscopy 
  • Thyroid ultrasound (this is usually done annually)

Additionally, your healthcare provider may recommend genetic counseling. It is highly recommended for people who have FAP and their relatives. For the person that has FAP, it can boost understanding of the condition, its implications, and help set realistic expectations of outcomes after treatment.

For relatives such as the children and other family members of the person with FAP, it can help them determine if they are at risk of having FAP and whether they need to undergo genetic testing. It can also help them emotionally support their loved one with FAP.

A Word From Verywell

Getting diagnosed with FAP can be overwhelming, especially when you consider the risk of developing colon cancer. However, with the right treatment and monitoring plan, you’ll be able to successfully navigate this condition. Speaking with family, friends, and even a therapist, if you are able to, can help you cope. Finally, if you plan on having kids in the future, you should make sure to attend genetic counseling with your partner beforehand. This way you can determine the risk to future children and evaluate your options.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Organization for Rare Disorders. Familial Adenomatous Polyposis.

  2. U.S. National Library of Medicine. Genetics Home Reference. Familial adenomatous polyposis.

  3. American Society of Clinical Oncology. Familial Adenomatous Polyposis.

  4. Waller A, Findeis S, Lee MJ. Familial adenomatous polyposis. J Pediatr Genet. 2016;5(2):78-83. doi:10.1055/s-0036-1579760

  5. Cleveland Clinic. Familial Adenomatous Polyposis (FAP): Inherited.

By Tolu Ajiboye
Tolu Ajiboye is a health writer who works with medical, wellness, biotech, and other healthcare technology companies.