Familial Adenomatous Polyposis (FAP): The Inherited Colon Condition That Causes Hundreds of Polyps — Screening, Surgery, and Lifelong Care
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Source currency note: This guide reflects medical information reviewed in May 2026. Always confirm current guidance with your healthcare professional.
TL;DR
Familial adenomatous polyposis (FAP) is a rare inherited condition that affects about 1 in 10,000 people. A change in the APC gene causes the colon and rectum to develop hundreds to thousands of polyps, usually starting in adolescence. Without treatment, the lifetime chance of colorectal cancer approaches 100%, often by age 40. The key point: early genetic testing, colonoscopy screening starting in late childhood, and surgery when polyps become unmanageable can prevent cancer entirely. FAP also raises the risk of other cancers and can cause features outside the colon, so care is lifelong and team-based.
Quick Answer
What is FAP? A rare inherited condition that causes hundreds to thousands of polyps in the colon and rectum, driven by a change in the APC gene.
What are the symptoms? Most people have no early symptoms. Later signs include blood in the stool, ongoing diarrhea, abdominal pain, unexplained weight loss, and anemia-related fatigue.
How serious is it? Without treatment, colorectal cancer is nearly certain, often by age 40. With screening and surgery, cancer can be prevented.
When does screening start? Colonoscopy typically begins in late childhood or early teens for people at risk, with upper endoscopy from about age 20 to 25.
How is it treated? Small polyps can be removed during colonoscopy early on, but surgery — removing some or all of the colon — is the main treatment, usually by the late teens or early 20s.
What is familial adenomatous polyposis (FAP)?
FAP is an inherited condition, meaning it is passed from parents to children through genes. It is rare, affecting about 1 in 10,000 people.
The condition leads to the development of hundreds to thousands of growths, called polyps, in the colon and rectum. These polyps typically begin to develop during adolescence and increase in number over time. Without treatment, the lifetime likelihood of colorectal cancer approaches 100%, often by age 40.
The good news: because FAP is predictable and detectable, screening and surgery can prevent cancer from developing at all. That is why families with FAP take screening seriously from childhood.
What causes FAP?
FAP is caused by a change — called a mutation or variant — in the APC gene. This gene normally helps regulate cell growth in the intestinal lining. When it works as expected, it helps prevent cells from growing too quickly.
When the gene is altered, that control is lost. Cells can grow and divide out of control, forming many polyps. Over time, some of these polyps can become cancer. The sheer number of polyps is what makes the cancer risk so high.
FAP is inherited, and a person only needs to inherit one copy of the altered APC gene to develop the condition. Each child of a parent with FAP has a 50% chance of inheriting it. In about 20% of people with FAP, the condition develops without a family history — the gene change appears for the first time in that individual (called a de novo variant).
Because FAP is caused by a genetic change, lifestyle or environmental factors do not cause the condition.
Key fact | Detail |
Inheritance pattern | One altered copy of the APC gene is enough |
Risk for each child of an affected parent | 50% |
Cases with no family history | About 20% (a new, first-time gene change) |
People affected | About 1 in 10,000 |
The milder form: attenuated FAP (AFAP)
FAP can vary in how it appears. Attenuated FAP (AFAP) is a milder form caused by changes in the same APC gene. It usually leads to fewer polyps, often fewer than 100, and the polyps tend to develop later in life. The likelihood of colorectal cancer remains high, but it is lower than in classic FAP. In some AFAP cases, surgery may be delayed or not needed right away.
In the past, terms such as Gardner syndrome and Turcot syndrome were used to describe FAP with features outside the colon. Today, these are generally considered part of the same condition rather than separate syndromes.
FAP symptoms: what to watch for
Most people with FAP do not have symptoms early on. Polyps can begin in childhood or adolescence, but they often cause no noticeable changes at first. As the number and size of polyps increase, symptoms may develop.
Symptom | What it looks like |
Blood in the stool | Visible blood or dark, tar-like stool |
Ongoing diarrhea or bowel habit changes | Persistent changes that do not resolve |
Abdominal pain | Unexplained and persistent |
Unexplained weight loss | Losing weight without trying |
Fatigue or weakness | Caused by anemia — a low red blood cell count |
Features outside the colon
Some people with FAP have physical features outside the colon that can appear before colon polyps are even found. These include skin changes, bony growths, dental changes, and eye findings. Rarely, symptoms related to other tumors may occur, such as headache or neurological symptoms linked to tumors of the central nervous system.
FAP complications and cancer risks
Beyond colon cancer, FAP raises the risk of several other complications, most related to polyp growth and increased cancer risk in other parts of the body.
Complication | What happens |
Small intestine cancer | Polyps in the upper small intestine — including the duodenum and the ampulla, where bile and pancreatic ducts enter — can become cancerous over time. |
Stomach polyps | Most do not become cancer, but some types carry a small risk. |
Desmoid tumors | Noncancerous growths that can develop in the abdomen or elsewhere, grow into nearby tissues, and sometimes cause serious issues. |
Other cancers | Higher likelihood of thyroid cancer, adrenal gland tumors, and cancers of the central nervous system. Less commonly, cancers of the liver or bile duct. |
When to see a doctor
Make an appointment with a healthcare professional if you or your child has any of the following: blood in the stool, ongoing diarrhea or a change in bowel habits, unexplained abdominal pain, unexplained weight loss, or persistent fatigue or weakness.
You should also seek care if you have a family history of FAP or early-onset colorectal cancer. If a parent, sibling, or child has FAP, talk with your healthcare team about genetic testing and screening. Early testing can guide care and reduce the risk of cancer.
Children and teens at risk of FAP should be evaluated early — screening and testing often begin in late childhood or the early teen years.
How is FAP diagnosed?
FAP may be suspected based on family history or when multiple polyps are found in the colon. A person is at risk if a parent, child, brother, or sister has the condition. For those at risk, regular screening often begins in childhood, because ongoing exams can detect polyp growth early, before cancer develops.
Genetic testing
A diagnosis of FAP can be confirmed with genetic testing, which looks for the variant in the APC gene. The test is usually done with a blood sample. Genetic testing is recommended for people with many colon polyps, people with a family history of FAP, and the children and blood relatives of someone diagnosed with FAP. Testing confirms the diagnosis and helps identify other family members who may be at risk.
Colon and rectum screening
Screening tests look for polyps in the colon and rectum and often begin in late childhood or the early teenage years for those at risk. A colonoscopy uses a flexible tube with a camera to look at the entire colon and is usually repeated every 1 to 2 years to monitor for new polyps. A sigmoidoscopy, a similar test, examines the lower part of the colon and is especially used in younger people.
Upper gastrointestinal screening
Because polyps can also develop in the stomach and small intestine, screening may include an upper endoscopy — a flexible tube used to look at the esophagus, stomach, and duodenum. This testing typically begins in early adulthood, around age 20 to 25, and is repeated at intervals based on the findings.
Additional tests
Other tests may be recommended to check for related conditions. A thyroid exam and ultrasound look for thyroid changes, and imaging tests such as CT or MRI may be used to check for desmoid tumors.
Treatment: how FAP is managed
Treatment for FAP focuses on reducing the risk of cancer and managing polyp growth.
Early in the condition, small polyps found during colonoscopy may be taken out. Over time, however, the number of polyps usually increases and becomes too large to manage individually, often by the late teens or early 20s. At that point, surgery is recommended to prevent colorectal cancer. Surgery may also be needed if a polyp becomes cancerous.
The three main surgeries
Surgery is the main treatment for FAP because of the high likelihood of colorectal cancer. The goal is to remove the at-risk tissue while preserving quality of life.
Surgery | What happens | When it is used |
Colectomy with ileorectal anastomosis | Removes the colon but keeps the rectum; the small intestine is connected to the rectum. | When the rectum has fewer polyps and can be managed with ongoing screening. |
Proctocolectomy with ileal pouch-anal anastomosis (J-pouch) | Removes both the colon and rectum. A pouch is created from the small intestine and connected to the anus, so stool passes normally without an abdominal opening. | When the rectum also needs to be removed but an ostomy can be avoided. |
Proctocolectomy with ileostomy | Removes the colon and rectum; the end of the small intestine is brought to an opening in the abdomen, and waste is collected in a bag outside the body. | When the other options are not suitable. |
The type and timing of surgery depend on the number, size, and features of the polyps, as well as individual preferences and overall health.
Medications
Medicines may help lessen the number of polyps or slow their growth, but they are most often used alongside surgery and screening, not as a replacement. Nonsteroidal anti-inflammatory drugs such as sulindac or celecoxib may reduce the number and size of polyps — a use considered off-label. These medicines do not eliminate cancer risk and do not replace surgery. Other medicines, such as targeted therapies, may be used for related conditions like desmoid tumors.
Treatment of related conditions
Polyps in the upper small intestine may be removed by endoscopy or surgery, especially if their features increase cancer risk. Desmoid tumors are often treated first with medicines, with chemotherapy or surgery considered if tumors cause symptoms or keep growing. Bone growths (osteomas) may be removed if they cause pain or for cosmetic reasons.
Lifelong screening, even after surgery
Even after treatment, regular screening remains necessary. The remaining rectum or surgically created pouch is regularly checked for new polyps, endoscopy monitors the stomach and small intestine, and additional exams such as thyroid evaluation or imaging may be recommended based on individual risk.
Coping and support
Living with FAP can be challenging — it often requires lifelong screening, medical care, and, for some, surgery. These steps can help.
Work with a healthcare team experienced in hereditary cancer conditions, including specialists in gastroenterology, surgery, and genetics. Stay on track with screening so changes are caught early. Learn about the condition to help with decision-making and reduce uncertainty. Seek emotional support from a counselor, psychologist, or support group, especially when facing major treatment decisions. Talk with family members — because FAP is inherited, sharing information with blood relatives can help them understand their own risk and consider testing. Consider genetic counseling to help explain testing, results, and what they mean for your family.
Preparing for your appointment
Being prepared helps you get the most from visits about FAP. Gather family history — bring information about parents, grandparents, and siblings who have had colon polyps, colorectal cancer, or related conditions, including their age at diagnosis if known. List your symptoms and concerns, even ones that do not seem related, and write down your questions. Bring prior test results from any colonoscopies, imaging, or genetic testing. Make a list of all medicines, vitamins, and supplements. Consider bringing a family member or friend to help remember information and provide support.
Useful questions to ask include: What tests do you recommend to confirm or monitor FAP? How often should I have screening? What treatment options are available, and when might surgery be needed? Should I consider genetic testing? What does this mean for family members?
Conclusion and next steps
FAP is a serious inherited condition, but it is also one of the most preventable causes of colorectal cancer — because the path from gene change to cancer is predictable, families who act early can stop cancer before it starts.
If colon cancer or hundreds of colon polyps appear in your family, the most important step is genetic testing and early screening. At-risk children and teens should be evaluated early, with colonoscopy typically starting in late childhood. Talk with your healthcare team about testing if a parent, sibling, or child has FAP, and share what you learn with your relatives — each of them carries a 50% chance of inheriting the same gene change if a parent is affected. Bring a family history summary, prior test results, and a written symptom list to your appointment, and ask specifically about screening frequency and surgical timing for your situation.
Frequently Asked Questions
Is FAP inherited?
Yes. FAP is passed from parents to children through genes. Each child of an affected parent has a 50% chance of inheriting the altered APC gene — though only one copy is needed to develop the condition. In about 20% of cases, the gene change appears for the first time with no family history.
What are the symptoms of FAP?
Most people have no early symptoms. As polyps grow in number and size, symptoms can include blood in the stool, ongoing diarrhea or bowel habit changes, abdominal pain, unexplained weight loss, and fatigue or weakness from anemia. Some people also have bone growths, dental changes, skin cysts, or eye findings.
Can FAP cause cancer?
Without treatment, the lifetime chance of colorectal cancer approaches 100%, often by age 40. FAP also raises the risk of cancers in the small intestine, stomach, thyroid, adrenal glands, and central nervous system. With early screening and surgery, cancer can be prevented.
How is FAP diagnosed?
A blood test for the APC gene variant confirms the diagnosis through genetic testing. Colonoscopy — often starting in late childhood or early teens for those at risk and repeated every 1 to 2 years — finds and monitors polyps. Upper endoscopy, thyroid exams, and imaging check for related risks.
What are the surgery options for FAP?
The main options are removing the colon while keeping the rectum (ileorectal anastomosis), removing the colon and rectum with a J-pouch, or removing them with an ileostomy. Surgery is usually recommended by the late teens or early 20s when polyps become too numerous to remove individually.
Can FAP be treated with medicine instead of surgery?
No. Medicines such as certain NSAIDs may reduce the number and size of polyps, but they do not eliminate cancer risk and do not replace surgery. Medicines are used alongside, not instead of, surgery and screening.
What does an FAP diagnosis mean for family members?
Blood relatives — parents, siblings, children, and even cousins — may carry the same gene change and should consider genetic testing. Sharing your diagnosis with family can help them detect risk early and start screening on schedule.
References
This article was prepared for general information only and is not a substitute for professional medical advice.
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