Familial Adenomatous Polyposis (FAP)

Familial adenomatous polyposis (FAP) is a hereditary syndrome in which hundreds to thousands of polyps grow inside the colon and rectum. These polyps usually start to form during the teenage years and – if left untreated – almost always turn into colorectal cancer.

For individuals who have not had a colectomy, the average age that colon cancer develops is 39. If a person has had a colectomy, the risk for colon cancer is significantly reduced, but the risk depends on the type of colectomy and if the rectum is left in place.

For 25% to 30% of people with FAP, the condition is not inherited from a parent, and there is no family history of it. In other words, it comes unexpectedly with no prior history.

As with other genetic conditions, you can have a hereditary syndrome without a clear linkage to how or why you have it. Regardless of whether FAP has been passed down in the family or it results new in an individual, a person with FAP has a 50% chance to pass on the condition to their children.

What causes FAP and who has it?

A mutation or defect in the adenomatous polyposis coli (APC) gene causes FAP. The APC gene is responsible for making the instructions for the APC protein. When the APC protein is working properly, its role is to keep cells in line or under control, which prevents tumors from forming.

Although most people with mutations in the APC gene will develop colorectal cancer if they have not had a colectomy, the number of polyps and how quickly they turn into cancer depends on some factors, such as the location and mutation of the APC gene.

Occurring in approximately 1 in 10,000 people, FAP affects both males and females equally. It is responsible for less than 1% of cases of colorectal cancer.

For people with a parent, child, or sibling with FAP, their risks of having FAP is up to 50%. Since FAP is due to a gene mutation that is present at birth, it can’t be prevented. However, preventive surgery like colectomy can significantly reduce colorectal cancer risk, and increased screening can allow for earlier detection of other cancers.

Am I born with FAP?

You are born with FAP, so it’s not a condition that develops over time. But it’s critical to understand that if you have FAP, the increased risk for cancer and symptoms do develop over time.

As more polyps form, they may cause the same symptoms as colorectal cancer, such as:

  • Abdominal pain
  • Blood in the stool
  • Changes in bowel habits
  • Unexplained weight loss
  • Anemia

Other symptoms of FAP can include:

  • Dental issues
  • Connective tissue tumors
  • Tumors of the duodenum (small intestine), liver, bones, skin, and other tissues, which may be cancerous or noncancerous.

If you have FAP, it’s extremely important to proactively develop a screening schedule with your doctor.

Equally significant and worth noting: Since about a quarter of the population develops FAP as the result of a new genetic change and with no family history, people with symptoms noted above should seek medical advice and get screened for colorectal cancer as soon as possible.

If you have FAP, you have an extremely high risk of developing colorectal cancer at a younger age. You are also at increased risk of developing several other cancers (stomach, small intestine, pancreas, bile duct, liver, adrenal gland, thyroid, and brain).

Colorectal cancer screening if you have FAP

Here is what’s recommended for screening if you have FAP. As FAP also increases the risk for other cancers, additional screenings – such as upper endoscopy to look at the stomach and small bowel – are also recommended.

  • A high-quality colonoscopy every 12 months beginning at age 10–15 is the preferred/recommended screening for colorectal cancer.
  • Once polyps are found in the colon, an annual colonoscopy is recommended until/unless surgery to remove the colon takes place.
  • An annual colonoscopy is recommended if a colectomy is delayed.


Not everyone with FAP will undergo surgery; however, it’s a recommended step for most patients.

Some people with FAP have undergone a prophylactic subtotal colectomy and others have had a total colectomy to prevent colorectal cancer from developing.

Your age or other high-risk factors, including family history, polyp number, and precancerous changes in the polyps, determine when and if surgery will take place. While some individuals with FAP may be in their 20s or 30s when their doctor recommends colectomy, others may be in their teens.

While colectomy may feel extreme, here are some reasons doctors recommend it:

  1. Too many polyps. People with FAP may have hundreds to thousands of polyps throughout their colon. It may not be possible to remove every polyp. Surgery significantly reduces colorectal cancer risk.
  2. Inability to find all the polyps or risk of missing them: Polyps aren’t always visible or easily accessible during endoscopy or colonoscopy. Some may be hard to find, making it difficult to ensure they’re all removed.
  3. Polyps regrowing: New polyps may grow in the same site after initial polyps have been removed. This means people with FAP need frequent invasive procedures.
  4. Prevention: A colectomy removes the entire colon before cancer has a chance to develop, significantly reducing risk of colorectal cancer.

Without removal of the colon through a colectomy, there’s almost a 100% chance of the polyps turning into colorectal cancer.

Do I need genetic counseling or genetic testing for FAP?

Since FAP is a hereditary syndrome, you should strongly consider genetic counseling. A genetic counselor can explain and educate about FAP and what it means for you and your family.

Importantly, your counselor will review cancer risks and screening recommendations for FAP and the benefits of doing increased screening starting at a younger age. Genetic testing, which can be done through a saliva or blood test, may be offered.

While genetic counselors help individuals consider all of their options and choices, the patient always has the final decision.

A genetic counselor can also explain how your personal health history may impact others in your biological family and help you identify other family members who are at risk for FAP. A genetic counselor can also coordinate tests for you and/or your family members and notify you if anything changes regarding your test results.

A genetic counselor can provide advice, education, and tools to equip you for decision-making; they can also answer questions or concerns about FAP.

Are there varying degrees of FAP or are other genes involved?

Attenuated familial adenomatous polyposis (AFAP) is a less severe version of FAP. People with AFAP may experience it later than someone with FAP and may have 100 or fewer polyps. About 70% of people with AFAP will develop colorectal cancer if colon polyps are left untreated.

MUTYH-associated polyposis (MAP) is caused by mutations in the mutY homolog (MUTYH) gene. MAP, like AFAP and FAP, is a rare hereditary syndrome where people may develop 100 or fewer polyps, which likely may develop into colorectal cancer if left untreated. People with MAP may have an increased risk of developing other cancers as well.

While some of the features and cancer risks may be similar between AFAP and MAP, there are differences in screening recommendations and how the conditions are inherited. Because of this, genetic testing is extremely important to clarify the exact hereditary syndrome and what the risks are to other family members.

What should I do if I know or think I have FAP?

If someone has a family history of FAP, AFAP, or MAP remain proactive. Be sure to seek medical advice for a screening schedule based on family history or signs and symptoms. Also be sure to consider genetic testing.

Resources to find a genetic counselor and/or a GI clinic who has experience with FAP

Explore the following resources to locate a genetic counselor and/or a GI clinic with FAP:

Medical Review

Michelle Springer
Michelle Springer, MS, CGC

Institution University of Colorado Cancer Center

Last Reviewed: March 31, 2024
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