Familial adenomatous polyposis (FAP)

Your body is made up of tiny building blocks called cells. Inside every cell is a set of genes. These genes are the instructions the cell needs to work properly. If a gene is changed, it may not give the correct instructions anymore. A change in a gene is called a gene variant or mutation.

People with FAP have a variant in a gene called the APC gene.

FAP is usually diagnosed by genetic testing. A sample of blood is checked for an APC gene variant.

If you have a parent, brother or sister with FAP, you can have this test to check for the variant they carry. It is usually offered from about the age of 10 or 12. Your GP should refer you to a specialist genetic centre for this test.

You may have a relative who has hundreds of polyps, but genetic testing has not found an APC gene variant. In this case, a genetic test will not be possible for you. Instead, you will be offered bowel screening tests to look for signs that you may have FAP. 

People without FAP in their family may be diagnosed after tests or treatment for something else. For example, you may be offered genetic testing if a high number of bowel polyps are found during:

• routine bowel screening
• tests for bowel cancer symptoms
• treatment for bowel cancer.

There are different APC gene variants that cause FAP. Many, but not all, of them carry a very high risk of bowel cancer. There is a milder version of FAP called attenuated FAP (aFAP). This can also be caused by variants in the APC gene. The effect of FAP on other parts of your body may depend on the exact gene variant you have.

Sometimes a person has hundreds of bowel polyps, but genetic testing does not find a gene variant. This may be caused by a gene variant that experts currently do not know about. The person is usually treated as though they have a diagnosis of FAP.

Your genetics specialist will explain:

• what your genetic test shows
• how this is likely to affect your body
• how this may affect other people in your family.

We have more information about test results and genetic testing.

Without surgery to remove the large bowel, most people affected by FAP will develop bowel cancer. Your doctor will talk to you about your risk and the best age for you to have surgery. This may depend on:

• the type of APC gene variant you have
• your age
• your feelings about surgery and the risk of cancer
• the results of your bowel screening tests.

The thought of surgery may be stressful or difficult to cope with. Although surgery is very effective at preventing bowel cancer, there are risks and side effects. For some people, there may be a risk that surgery will affect their fertility. Your surgeon will explain what to expect and the risks and benefits of your surgery.

Sometimes surgery can be delayed, as long as you do not have too many polyps. If surgery is delayed, it is important to have a colonoscopy at a specialist centre every 6 to 12 months.

If you have any questions or worries, talk to your surgeon, nurse or FAP specialist. Sometimes it helps to talk to other people in the same situation. We have more information about getting support at the end of this page.

It may be possible to remove the colon and join the small bowel to the top of the rectum or the sigmoid (the section of bowel that joins the colon to the rectum). This operation is called an ileo-rectal or ileo-sigmoid anastomosis. 

After the operation, you will be able to go to the toilet normally, but will need to go more often. There is still a risk that polyps may develop in the rectum. You will need a test to check this every 6 to 12 months, depending on how many polyps are growing in the rectum.

Sometimes the lining of the rectum is also removed to avoid the risk of polyps forming there. If the rectum is removed, it may be possible to replace it with a pouch. This is made using a piece of the small bowel.

This is a complex operation and involves making a stoma. To make a stoma, the surgeon brings the end of the small bowel out on to the skin of the tummy (abdomen). You wear a bag over the small bowel opening. This collects stools (poo).

Having a stoma allows the joins that hold the pouch in place to heal. After about 3 months, you may have another operation to reverse the stoma. You will then be able to go to the toilet normally. But you will need to go more often than before. The stools you pass will be looser, and you might need to take anti-diarrhoea medicine. If the rectum has been removed, you will still need to have the pouch checked every year. This is because polyps can continue to grow there.

Sometimes the rectum is removed but it is not possible to replace it with an internal pouch. In this situation, you will have a permanent stoma.

It can take time to get used to having a stoma. There are specialist nurses who can help and support you through this. They are called stoma nurses.

Many people who find out they have a high cancer risk decide to improve their lifestyle in some way. Some people find a healthy lifestyle makes them feel they are doing everything they can to control their cancer risk.

It is not clear how much lifestyle factors affect cancer risk in people with FAP. But there is strong evidence a healthy lifestyle improves your general health and well-being. Ask your genetics specialist for advice about your risks. Your genetics specialist, GP or practice nurse can give you more information about healthy living.

FAP can be difficult to cope with. There is the uncertainty of not knowing whether you will develop cancer. There are often complicated decisions to make about the right time to have surgery. 

Some people choose to have screening for longer, because they find the thought of surgery very difficult. Other people may choose to have surgery earlier because they find waiting for each screening hard. 

It is important to talk to your FAP specialist, GP or nurse. They will be happy to answer any questions you have.

There is no right or wrong way to cope. But help is there if you need it. If you are struggling, talking about your feelings and worries may help. You may want to talk to a partner, family member or friend. You can also talk to our cancer support specialists for free on 0808 808 0000. Or you can share your thoughts with members of our Online Community.

Here are some other organisations you may find helpful:

• The Ileostomy and Internal Pouch Association (IA) gives support and information to anyone who has had their colon removed.
• PolyposisPatient is a support group for people with polyposis syndromes.
• St Mark’s Centre for Familial Intestinal Cancer supports people who have a polyposis condition and their relatives. It has an advice line for patients, family members and healthcare professionals. You do not have to be one of its patients to access this service. Call 020 8453 2656.