Familial adenomatous polyposis (FAP) is a hereditary syndrome that raises your risk of developing colorectal cancer to nearly 100%. Cancer develops from adenomatous colon polyps, which can appear in the hundreds to thousands. To manage this risk, most people with FAP will have their whole colon removed sometime in their early life.
Familial adenomatous polyposis is a genetic disorder that predisposes you to develop precancerous colon polyps called adenomas. Colon polyps are abnormal growths in the lining of your colon or rectum. They aren’t cancer, but certain types, like adenomas, can change into colorectal cancer.
Many people get a few colon polyps at random as they get older. But if you have a hereditary polyposis syndrome like FAP, you’ll develop many colon polyps — typically over a hundred — starting from a young age. This significantly raises your lifetime risk that one of them will become cancerous.
To manage this risk, healthcare providers usually recommend complete removal of the colon (total colectomy) and sometimes the rectum, too (proctocolectomy). Polyps in FAP appear too frequently to manage them one by one. Without surgery, most people with FAP will develop cancer by their middle-age years.
People with FAP may also develop polyps in other organs, and other abnormal growths in places like their skin, soft tissues, teeth and bones. Even after colectomy surgery, they’ll need to continue to have regular screenings for other tumors, and possibly additional surgeries to manage those tumors.
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Without treatment, the risk of developing colorectal cancer with familial adenomatous polyposis is close to 100%. It also develops relatively earlier and faster with FAP than in those without. Children in families known to be affected by the syndrome begin yearly colonoscopy screenings at the age of 10.
Besides colorectal cancer, people with familial adenomatous polyposis also have an increased risk of developing other cancers, including:
Familial adenomatous polyposis has a classic form and some less common forms that are considered subtypes.
Familial adenomatous polyposis is rare, estimated to affect about 1 in 8,000 people. It accounts for only about 0.5% of all colorectal cancer cases. Variants like AFAP, Gardner syndrome and Turcot syndrome are rarer. They represent between 5% and 10% of all familial adenomatous polyposis cases.
Lynch syndrome is a different hereditary syndrome that can raise your risk of developing colorectal cancer and other cancers. Lynch syndrome is also sometimes called hereditary nonpolyposis colorectal cancer syndrome (HNPCC). As the name suggests, it doesn’t necessarily cause a lot of colon polyps.
People with Lynch syndrome may develop colorectal cancer with only one or a few colon polyps. Polyps and cancer also tend to develop a little later than in classic FAP, and the lifetime risk is a bit lower. Different gene mutations lead to the differences between Lynch Syndrome and FAP.
Colon polyps in FAP begin to appear much earlier than in the general population, often during the teenage years. They usually won’t cause symptoms until they’ve grown large enough to be dangerous. But if you have a colonoscopy for screening purposes, your healthcare provider will find them.
People with FAP often have hundreds or thousands of colon polyps. Those with AFAP have at least 20. The greater number and faster growth of polyps in FAP may make them more likely to cause symptoms than polyps usually are. Symptoms may include rectal bleeding, diarrhea or chronic abdominal pain.
People with FAP may also have superficial lesions that healthcare providers can observe, such as:
Colon polyps in FAP begin to appear at the average age of 16. They occur a little later with AFAP. If your parents and healthcare provider know that you’re at risk for the syndrome, they’ll likely begin screening after you turn 10. If they don’t know, it might be your symptoms that bring the condition to light.
Familial adenomatous polyposis is caused by a gene mutation. The gene is called adenomatous polyposis coli, or APC. It’s a tumor suppressor gene, which means it’s supposed to prevent cells from growing out of control and forming tumors. The mutation interferes with the function of the gene.
The gene mutation that causes FAP is a germline mutation, which means it occurs during conception, not during your lifetime. This is how it runs in families. If one of your parents has the mutation, you have a 50% chance of inheriting it. However, up to 30% of these mutations are original, not inherited. This means that about 30% of patients diagnosed with FAP won’t have a family history of the disease.
Colorectal cancer is the most important complication to manage with FAP. Surgery to remove your colon drastically lowers this risk. But living without a colon will complicate your life, to a lesser extent, by changing the way you poop. You’ll have to replace your colon with either an ileostomy pouch or an ileal pouch.
Since the gene mutation that causes FAP is in every cell of your body, tumors can also occur throughout your body. You may develop other tumors outside of your colon, which can sometimes become cancerous. Your healthcare provider will recommend a screening schedule to check for these tumors:
If you want to know if you’ve inherited the APC gene mutation, you can find out through genetic testing. A genetic test takes a DNA sample (such as blood or saliva) and looks for specific gene mutations. If you do have the mutation, the next step is a colonoscopy to check for adenomas.
Diagnosis of FAP is based on having at least 100 polyps, or 20 for AFAP, and the APC mutation. Familial adenomatous polyposis isn’t the only hereditary syndrome that can cause adenomatous colon polyps. MUTYH-associated polyposis is a similar syndrome caused by a different mutation, in the MUTYH gene.
Treatment for FAP involves lifelong surveillance and, eventually, surgery. In the beginning, if you have fewer polyps (or AFAP), your provider might be able to remove them individually during colonoscopy screenings (polypectomy). You’ll need surgery when there are too many or they become cancerous.
Most people with classic FAP will have a total colectomy sometime in their late teens to early thirties. Your healthcare provider will determine when to schedule your surgery based on your particular risk factors. They’ll also discuss with you the different types of colectomy operations you might have.
When you have your colon removed, there will be a gap between your small intestine and your rectum (or anus). Sometimes, a surgeon can reconnect these ends together so you can continue pooping out your anus (butthole). If not, they’ll create an ostomy, a new opening in your abdomen for your poop to come out.
Your healthcare team will advise you on how often to get screening tests for different types of tumors based on your personal risk factors. For classic FAP, guidelines recommend yearly colonoscopies starting at age 10 and continuing until your colectomy. For AFAP, yearly screenings should begin by age 20.
After your colectomy, you’ll need to continue with regular sigmoidoscopies, examinations of the end of your GI (gastrointestinal) tract. If you have some rectum left over, it should be checked every six to 12 months. If your rectum was removed but was replaced by an ileal pouch, it should be checked every one to four years.
Other regular screenings may include:
Genetic counseling can help you understand the risks of passing on FAP to your genetic descendants. Discussing these risks can help you plan. In general, you can’t prevent the gene mutation from happening at conception, but there are some different family planning options you can consider.
Without timely treatment, the median life expectancy is 42 years. But with appropriate care, you can live a normal life. Once your colon has been removed, your biggest risk is from other gastrointestinal cancers or problematic desmoid tumors. These occur much less frequently than colorectal cancer.
If you’re diagnosed with FAP, you can expect a lifetime of medical screenings and possibly multiple surgeries to remove tumors. Tumors outside of your colon are less likely to become cancerous than colon polyps. Desmoid tumors, which aren’t cancerous, can be a minor irritation or a major one.
You can expect to have a total colectomy sometime in your early life. You may be able to have your bowels reconnected afterward, or you may have an ileal pouch or an ostomy. All options come with some risks of specific complications. But you can live a long and healthy life after a colectomy.
A note from Cleveland Clinic
It’s certainly upsetting to learn you have a genetic disease that’ll require lifelong care. But once you know, you can take the necessary steps to manage your cancer risk. While surgery is almost certainly in your future, healthcare providers try to cause as little disruption to your life as possible.
Many people are able to have minimally invasive colectomy surgery using laparoscopic techniques, which means small incisions and a shorter recovery time. Those who will have an ileal pouch created will need multiple surgeries, but in the end, they’ll be able to use the bathroom as they did before.
Last reviewed by a Cleveland Clinic medical professional on 09/21/2023.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy