What is familial adenomatous polyposis (FAP)?

FAP is a rare condition that can run in families. It causes hundreds or thousands of small growths in the large bowel. These are called polyps (or adenomas). They usually start to appear when a person is in their teens. If the polyps are not treated, one or more of them will almost certainly develop into cancer (usually by the age of 40). To prevent this, many people affected by FAP decide to have surgery to remove the large bowel.

There are also other conditions that can cause different types of bowel polyps to grow. These conditions also run in families. They include:

  • MUTYH-associated polyposis (MAP)
  • juvenile polyposis syndrome
  • Peutz-Jeghers syndrome
  • serrated polyposis syndrome.

These conditions are extremely rare. Your specialist doctor can give you more information if you need it.

FAP and other parts of the body

FAP can also affect other parts of the body. This may include:

  • harmless black dots on the back of the eye called CHRPE (congenital hypertrophic retinal pigment epithelium)
  • harmless lumps on the bones called bony osteomas
  • harmless lumps on the skin called sebaceous cysts
  • polyps in the stomach and duodenum (the first part of the small bowel) that may develop into cancer
  • a type of benign tumour called a desmoid tumour
  • more rarely, cancer in other parts of the body.

How FAP causes cancer

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. Sometimes the structure inside a gene is permanently changed, so the gene no longer gives the correct instructions. This change is called a gene mutation.

People with FAP are born with a mutation in a gene called the APC gene. By itself, the APC gene mutation does not cause cancer. But over a person’s lifetime, more mutations build up. Eventually, gene mutations in a cell may mean the cell stops working normally. Cancer develops when cells like this can multiply in an abnormal way and grow out of control.

For a person with FAP, the gene mutation they are born with means they are almost certain to develop bowel cancer. They may also have a higher risk of developing certain other types of cancer.

We have more information about gene mutations and how cancer develops.

How FAP runs in families

Genes are passed from parent to child (inherited) when a sperm and egg join to start a pregnancy (conception). We have more information about how genes are passed on.

We have two copies of each gene – one from our mother and the other from our father:

  • the sperm contains one copy of the father’s genes
  • the egg contains one copy of the mother’s genes.

If one parent has an APC gene mutation, either you will get the copy containing it, or you will not. There is a 1 in 2 (50%) chance the gene mutation is passed on.

The image shows a female and male figure. A pair of genes is shown beside each figure. The female has two green genes shown side by side. The male figure has a green gene and a red gene shown side by side. The red gene is the gene mutation.

About 1 in 4 people with FAP (25%) are the first in their family to have the gene mutation. This means your parents did not have it. Any children you have will still have a 1 in 2 (50%) chance of inheriting it from you.

Diagnosing FAP

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

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

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

People with no 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:

Understanding genetic test results

There are different mutations that can affect the APC gene and cause FAP. All of them carry a very high risk of bowel cancer. The effect of FAP on other parts of your body may depend on the exact gene mutation you have.

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.

Screening and FAP

Screening uses tests to:

  • find cancer at an early stage when it can be treated most effectively
  • find and treat changes that are likely to develop into cancer.

Your doctor will explain what tests you need, when and how often. It is important to keep having screening unless genetic testing shows you definitely do not have the gene mutation that affects other people in your family.

Bowel screening

If you have FAP, you will be offered regular bowel screening from about the age of 12. This involves having a test called a colonoscopy to look at the inside of the bowel. If the number of polyps are increasing, this may be a sign that surgery is needed.

Sometimes, another test called a flexible sigmoidoscopy is also used to check the inside of the rectum.

Stomach and small bowel screening

People affected by FAP also have a risk of developing cancer in the stomach or small bowel. The risk is much lower than for bowel cancer. Most people are offered a test called an upper endoscopy to look for early signs of cancer in these areas. This is usually done from around the age of 25. Your specialist can tell you how often you will have this test.

Screening for other cancers

Your risk of other types of cancer linked to FAP is much lower than your risk of bowel cancer. There are currently no effective screening tests for these other types of cancer.

Sometimes, screening for other types of cancer is offered as part of a research trial. Taking part in a research trial is completely up to you. Your doctor or nurse can explain the possible risks and benefits of taking part.

Bowel surgery for FAP

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 mutation you have
  • your age
  • your feelings about surgery and the risk of cancer
  • the results of your bowel screening tests.

Most people are advised to have surgery between the ages of 16 and 25. The thought of this may be stressful or difficult to cope with. Although surgery is very effective at preventing bowel cancer, there are risks and side effects. 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 being delayed, it is important to have a colonoscopy at a specialist centre every year.

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.

Removing the colon

It may be possible to remove the colon and join the small bowel to the top of the rectum or the sigmoid. This is called an ileo-rectal or ileo-sigmoid anastomosis. You will be able to go to the toilet normally, but will need to go more often than before. 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.

Removing the colon and the rectum

Sometimes, the lining of the rectum is also removed to avoid the risk of polyps forming there. If the rectum is removed, a pouch to replace it can usually be 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). A bag is worn over the opening to collect bowel movements (poo).

Having a stoma allows the joins that hold the pouch in place to heal. After about 3 months, you may be able to 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. You might need to take anti-diarrhoea medicine. Although the rectum has been removed, you will still need to have the pouch checked every year. This is because sometimes polyps can continue to grow there.

A very small number of people have the rectum removed, but it is not possible to replace it with an internal pouch. Instead, they have a permanent stoma.

It can take a while to get used to having a stoma. There are specialist nurses (stoma nurses) who can help and support you through this.

Know your body

If you know your body and what is normal for you, it will help you be aware of any changes. If you notice a change in how you feel or how your body works, it is better to be safe and get it checked. Always see your GP or your FAP specialist if you have symptoms that are ongoing or unusual for you.

We have more information about the signs and symptoms of cancer that you may find helpful.

Health and lifestyle

There may also be factors in your lifestyle that affect how polyps and cancer develop.

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.

There is not always clear evidence about how much lifestyle factors affect cancer risk in people with FAP. However, there is strong evidence they improve 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.

Planning a family

If you have FAP, there is a 1 in 2 (50%) chance that any child you have could inherit it from you. You may have questions about this if you are planning to get pregnant or start a pregnancy. Your genetics specialist can talk to you about this if you have questions.

We have more information about planning a family and inherited cancer risk.

Your feelings

FAP can be very 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 on 0808 808 00 00. Or you can share your thoughts with members of our Online Community.

Here are some other organisations you may find helpful.

  • The FAP Gene Support Group
    The FAP Gene Support Group offers non-medical support and information about FAP.
  • IA (the Ileostomy and Internal Pouch Support Group)
    IA gives support and information to anyone who has had their colon removed.
  • PolyPeople
    PolyPeople is a support group for people with polyposis syndromes.
  • The Polyposis Registry
    The Polyposis Registry supports people who have a polyposis condition and their relatives. It runs an advice line for patients, family member and healthcare professionals. You do not have to be one of its patients to access this service. Call 020 8235 4255.