Familial adenomatous polyposis (FAP) is a rare condition that predisposes you (makes you more susceptible) to precancerous colorectal adenomatous polyps. Adenomatous polyps are abnormal growths that look similar to the lining of your intestines. Colorectal means they grow in your large intestines and your rectum, the area at the end of your intestines.

FAP occurs in roughly 1 in 8,000 to 18,000 people in the United States. It’s usually inherited from your parents, but it’s also possible to develop it if neither of your parents carries the gene mutation that causes FAP.

FAP usually requires the removal of part or all of your large intestines. If left treated, it almost always leads to colorectal cancer at a relatively young age. According to 2014 data from NORD, it’s responsible for about 1 in 200 cases of colorectal cancer.

Read on to learn more about this rare condition, including symptoms, diagnosis, and treatment.

FAP is an inherited condition that makes you more likely to get precancerous adenomatous colorectal polyps. People with FAP develop hundreds to thousands of these polyps along their rectum and colon. About 40 cases of FAP are thought to occur per million people.

Polyps develop between the ages of 7 to 36, and the average age of development is 16. If left unrecognized and untreated, they almost always turn into colorectal cancer by your 30s or 40s.

Other names of FAP

FAP goes by several other names. They include:

  • adenomatous polyposis of the colon (APC)
  • hereditary polyposis coli
  • multiple polyposis of the colon
  • familial multiple polyposis
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FAP variations

FAP is divided into subtypes depending on its particular features. These subtypes include:

  • Classic FAP: Classic FAP is usually diagnosed when there are 100 or more polyps and you have the classic signs of the disease.
  • Gardner syndrome: Gardner syndrome is when tumors also develop outside of the gastrointestinal tract. These tumors can include:
    • fibromas: noncancerous tumors made up of connective tissue
    • desmoid tumors: noncancerous tumors that grow in connective tissue and often appear in the abdomen, shoulders, upper arms, and thighs
    • osteomas: noncancerous tumors found on bone
  • Attenuated FAP: Attenuated FAP is when there are between 10 and 99 polyps. People with attenuated FAP tend to develop polyps and cancer later than people with classic FAP.
  • Turcot syndrome: FAP is classified as Turcot syndrome in people who have both colorectal polyps and central nervous system tumors.

The primary sign of FAP is the development of hundreds to thousands of polyps. Common symptoms can include:

People with FAP can also develop:

  • severe dehydration from electrolyte imbalances caused by diarrhea and mucous discharge
  • obstructed flow of bile, which can cause jaundice and other symptoms
  • obstructed flow of pancreatic enzymes, which can cause acute pancreatitis

Some people may also develop:

  • polyps in the stomach and small intestines
  • osteomas
  • teeth abnormalities
  • congenital hypertrophy of the retinal pigment epithelium, a rarely symptomatic noncancerous growth of the retina that affects 70% to 80% of people with FAP
  • soft tissue tumors

FAP is caused by a genetic mutation in the APC gene. APC is a dominant gene, meaning that there’s a 50% chance of developing FAP if one of your parents has it. According to one estimate, about 50,000 American families carry the gene.

The risk is the same in people assigned male at birth and people assigned female at birth. It can affect people of any ethnicity.

About 10% to 30% of people develop FAP due to spontaneous mutations in this gene without a family history.

Diagnosis of FAP is fairly easy since people with symptoms can have thousands of polyps that show up with a colonoscopy.

A colonoscopy is an exam in which a doctor examines the inside of your colon by inserting a thin tube with a camera into your anus. If they only examine the lower part of your colon, it’s called a sigmoidoscopy.

Classic FAP is usually diagnosed if you have 100 or more polyps. It may also be diagnosed if you have fewer than 100 polyps if you:

  • are young
  • have had part of your bowel removed
  • have a relative with classic FAP

A blood test can confirm whether you’re carrying an APC mutation that’s been linked to FAP. The results of a genetic test may also help you understand your risk of complications.

Partial or complete colectomy, or removal of your colon, is usually recommended for people with FAP. It’s usually performed between your late teens and late 30s.

Surgery doesn’t cure FAP but can lower the risk of developing cancer. Polyps can still develop in other parts of your rectum, colon, or small intestines even after surgery.

The nonsteroidal anti-inflammatory drug (NSAID) sulindac that’s usually used to treat arthritis is sometimes prescribed to treat polyps in the rectum.

When removal is recommended

Removal of polyps in the lower part of the small intestines is often recommended if:

  • they cause symptoms
  • they’re large
  • a doctor thinks there’s a high chance that they’ll become cancerous

Other treatments

Desmoid tumors that are compressing your organs can be treated with:

FAP isn’t preventable since it’s an inherited condition. However, regular screening can improve the outcomes and lower your risk of developing advanced cancer.

The American Academy of Family Physicians recommends the following screening protocols for people with FAP:

  • sigmoidoscopy starting at around 10 years of age
  • yearly sigmoidoscopy or colonoscopy once an APC mutation has been found
  • yearly colonoscopy once polyps are found until a colectomy procedure is scheduled
  • continued yearly screening until 24 years of age
    – screening every 2 years until age 3
    – screening every 3 years until age 44
    – screening every 3 to 5 years after age 44
  • annual thyroid exam, possibly with ultrasound, at 20 to 25 years of age
  • colonoscopy and upper endoscopy starting at 20 to 25 years of age for those without an APC mutation

Results of current research trials

Researchers are continuing to examine better ways to screen and treat FAP. Some current clinical trials are examining the effectiveness of:

  • azithromycin
  • niclosamide
  • low dose lithium
  • eicosapentaenoic acid
  • personalized surveillance and intervention protocols
  • encapsulated rapamycin

You can find current clinical trials on the National Library of Medicine website. A doctor can also help you find clinical trials that you may be eligible for.

Without a colectomy, people with FAP usually develop colorectal cancer in their 30s or 40s, and the average age of development is 39 years. The average age of death in people without surgery is 42 years. The most common causes are metastatic colorectal cancer and desmoid tumors.

Life expectancy is significantly higher in people who receive a colectomy. Regular screening is also associated with better outcomes.

About 10% of people with FAP develop other cancers in their:

  • small intestines
  • thyroid
  • pancreas
  • liver
  • central nervous system
  • bile ducts

About 5% of people experience significant symptoms or death from desmoid tumors.

FAP is a genetic condition that causes the development of hundreds to thousands of polyps in your colon and rectum.

People with FAP almost always develop colon cancer in their 30s or 40s if they don’t receive surgery to remove part or all of their colon.

Regular screening for cancer is critical for improving outcomes. A doctor can advise you about how often you should get screened and whether you’re eligible for clinical trials that may give you access to new treatments.