Familial adenomatous polyposis (FAP)

Familial adenomatous polyposis (FAP) is a rare condition that can run in families. It can also affect people who do not have a family history of it. FAP causes hundreds or thousands of small growths called polyps to grow in the large bowel. If these polyps are not treated, some of them are likely to develop into cancer.

If you have a family history of FAP, you will have regular tests for it from a young age. This is likely to include a procedure called a colonoscopy. It may also include genetic testing to look for the FAP gene. If you do not have a family history of FAP, you may have bowel symptoms that lead to diagnosis. Talk to your GP if you are worried about any symptoms you have noticed.

With early treatment, people with FAP can avoid bowel cancer and lead healthy lives. Treatment usually involves surgery to remove part, or all, of the large bowel.

Having FAP, and needing surgery for it, can be distressing. There is lots of support available for you.

What is familial adenomatous polyposis (FAP)?

FAP is a rare condition that can run in families. Conditions that run in families are called inherited or familial. People with FAP are very likely to develop bowel cancer if they do not have treatment. About 1 in every 100 of all bowel cancers is linked to FAP.

FAP can also affect people who do not have a family history of it. This happens in about 1 in 4 people with FAP.

People with FAP have hundreds or thousands of small growths called polyps in their large bowel. These polyps are sometimes called adenomas. This is where the ‘adenomatous’ part of the name FAP comes from. Polyposis means lots of polyps.

The polyps 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). There is a type of FAP called attenuated FAP where the polyps appear about ten years later than with the usual FAP.

Most people with FAP are offered the option of having an operation to remove the large bowel when they are young. This can be hard to cope with, but it means they can avoid getting bowel cancer.

The large bowel

The bowel is part of our digestive system. It is divided into two parts – the small bowel and the large bowel. The large bowel is made up of the colon and rectum.

The food we eat passes from the stomach, where it is digested, into the small bowel. The small bowel is where our bodies absorb the essential things we need from our food. The digested food then moves into the large bowel where water is absorbed and waste or stools are formed.

The first part of the large bowel that runs upward is called the ascending colon. It then goes across to the left side of the abdomen (the transverse colon) and down to the bottom of the abdomen (the descending colon). It ends with the sigmoid colon, the rectum and then the anus.

The bowel
The bowel

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FAP and other parts of the body

FAP can affect other parts of the body. Most people have some harmless changes, such as black dots to the back of the eye (retina). These black dots do not affect your vision at all and often help to diagnose FAP.

Some people get harmless lumps that affect the bones, or cysts on the skin.

You can also get polyps in the stomach and duodenum (sometimes called the first part of the small bowel). The polyps in the stomach are often a harmless type called a fundic gland polyp. Very occasionally adenomas can grow in the stomach, and these polyps should be removed. A close check will be kept on the duodenum as most people with FAP will develop adenomas here. Screening of the upper gastrointestinal tract usually begins at the age of 25. How often you are screened depends on the number and size of polyps seen. Your doctor will normally use a staging system called Spigleman Staging to help decide how often you are screened. This is usually once a year, three times a year or five times a year.

FAP increases the risk of getting cancer in other parts of the body, especially in the duodenum and thyroid. You may have regular tests to check for this.

If you have FAP, you also have a higher risk of developing a rare tumour called a desmoid tumour. It affects about 10% of patients with FAP and usually develops in the abdomen or abdominal wall. Desmoid tumours are classified as benign tumours, which means they are not cancer. Desmoid tumours do not tend to spread to other parts of the body, but can spread into nearby tissues. Because of this, they are usually treated in a similar way to cancerous sarcomas.

How FAP is inherited

FAP is caused by a fault in a gene called the APC gene. Our genes carry the information that is passed on (inherited) from our parents. They decide things like the colour of our eyes and affect the way our bodies grow, work and look.

We have two copies of each gene – one from each of our parents. If someone has FAP, it means they have one healthy APC gene and one altered one.

If that person has a child, there is a 50% chance that they will pass on the altered gene. This is because only one copy of a gene is passed on from each parent. If a child inherits the altered gene, they will develop FAP. This is known as a dominant inheritance pattern, and for this reason FAP is known as a dominantly inherited condition.

If you have a parent, brother or sister with FAP, you can have a blood test to find out whether you have inherited the altered gene. Your GP will need to refer you to a specialist centre. This test is usually offered from the age of 12 to 14. Some families have been given a clinical diagnosis of FAP where a genetic alteration has not been found. If this happens, you will be offered bowel screening at a similar age. There are other forms of adenomatous polyposis and your specialist centre should give you more advice about these.

In about 1 in 4 people with FAP, an altered APC gene occurs without a family history of FAP. Their children will also have a 50% chance of inheriting the altered gene.

Symptoms of FAP

You can have hundreds of polyps in your bowel without any symptoms. If these polyps go untreated, symptoms may eventually appear. In some people, there are no symptoms until a polyp has changed into a cancer. The average age of bowel cancer developing in someone with untreated FAP is 39, but it can happen in people aged as young as 17.

Some of the symptoms of FAP and bowel cancer are:

  • blood or mucus in the stools, or bleeding from the back passage
  • diarrhoea or constipation (a change in the normal bowel habit that lasts longer than six weeks)
  • pain in the tummy (abdomen) or back passage
  • weight loss for no obvious reason.

These symptoms can be caused by conditions other than FAP or bowel cancer. It is always important to get them checked out by your doctor if they last for longer than a few days.

Genetic testing

It is possible to find out whether you have the altered FAP gene by doing a genetic blood test.

First, the test is carried out on a member of the family who has FAP. When their altered gene has been found, other family members can be tested to find out whether they have the same altered gene. If the genetic test shows that you do not have the altered gene, there is no reason for you to have bowel screening. If you have not inherited the altered gene, your risk of getting bowel cancer is the same as someone without FAP.

Sometimes the altered gene cannot be found in a person who has multiple adenomas (polyps). This means that their close family cannot have a genetic test but they will still have regular bowel checks (screening).

Before genetic testing, you will be offered counselling. This will help you understand the results and what they mean for you and your family.

Screening after being diagnosed with FAP

When you have been diagnosed with FAP, you will have regular bowel checks until surgery is needed. You will also have a test called an oesophagogastroduodenoscopy (OGD). The test is usually done every 1 to 5 years and it is to check the stomach and duodenum (also known as the upper GI tract). This is because most people with FAP develop polyps in the duodenum. These tests usually start from the age of 25.

You can stop having screening tests if genetic testing shows that you do not have a copy of the altered gene. Otherwise, it is very important to carry on with your yearly bowel checks.

If you have a type of FAP called attenuated FAP, you will have regular tests (screening) for longer. You have fewer polyps and so bowel cancer usually develops later. Because of this you may be screened for a longer time before deciding to have surgery.

It is very important to carry on having all your tests until you have made a decision about surgery. Your surgeon will talk to you about which operation would be best for you.

Having a colonoscopy

A colonoscopy is a way of examining the lining of the bowel from the inside. The procedure is usually done in the hospital outpatient department and takes about an hour. It is the most thorough and effective way of diagnosing bowel cancer. The colonoscopy can also see whether there are any polyps in your bowel.

The bowel has to be completely empty for a colonoscopy. This means following a careful diet for a few days before your test. You will also need to take laxatives, which the screening centre or hospital pharmacy will provide. The department carrying out your colonoscopy will give you instructions about your diet, and about exactly when to take your laxatives.

Shortly before the colonoscopy, you may be given a sedative to help you feel relaxed. Once you are lying comfortably on your side, the nurse or doctor will gently pass a thin flexible tube (a colonoscope) into your back passage. The tube is made up of flexible fibres so it can easily pass around the curves of the bowel. A tiny light and camera on the end of the tube are used to show any abnormal areas.

During the colonoscopy, photographs and samples (biopsies) of the cells on the inside of the large bowel can be taken. Most polyps can be painlessly removed using a wire loop that is passed down the colonoscope. A colonoscopy can be uncomfortable, but the sedative will help you feel more relaxed.

Most people are ready to go home a couple of hours after their test. You will need to arrange for someone to collect you from the hospital as you should not drive for several hours after a sedative. You should also have someone with you for about 12 hours afterwards.

Sometimes it is not possible to see the whole bowel during a colonoscopy. This can happen if the bowel is not completely empty or if the colonoscope can't pass around a bend in the bowel to reach the end. If this happens, you may be asked to have another colonoscopy or a CT colonogram.

Treatment for FAP

If you are very young or if the polyps look harmless, you might continue to have regular bowel checks for a while. When there are lots of polyps in the bowel, it is impossible to know when one might become a cancer. An operation is the safest way to treat FAP and prevent bowel cancer.


Removing the colon

It may be possible to remove the colon and join the small bowel to the top of the rectum. This is called an ileo-rectal anastomosis (IRA). 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 removed to avoid the risk of polyps forming there. If the rectum is removed, a pouch to replace it can be made using a piece of the small bowel. This is a complex operation. After the surgery, you will 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, yearly checks of the pouch will still be needed as sometimes polyps can continue to grow here.

Having a stoma

A very small number of people will need to have the rectum removed, and will be unable to have an internal pouch formed. The end of the small bowel is brought out on to the skin of the tummy (abdomen). The opening is called a stoma and a bag is worn over it to collect bowel motions. 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.

Having surgery for FAP can be very distressing. But it is the best way to stop you from getting bowel cancer.

Videos you might find helpful

  • Having a stoma: A clinical nurse specialist in stoma care talks about having surgery for rectal cancer and living with a stoma.
  • Pat's story: Pat talks about her experiences of living with a stoma after surgery for rectal cancer.

Pre-implantation genetic diagnosis (PGD)

This is a specialised technique that can help couples affected by FAP to have a child who does not have the FAP gene. Some people may want to consider this when planning their family.

PGD involves checking the genes of embryos (fertilised eggs) that have been made by IVF (in vitro fertilisation) treatment. A single cell is taken from each embryo and is checked for the altered gene that causes FAP. Only embryos that are unaffected by the gene are then implanted in the womb. If a baby develops from the embryo, it should not have FAP.

There are many things to consider if you are thinking about having PGD. For example, very occasionally testing may miss the altered FAP gene, or sometimes embryos may be damaged in the process. PGD is not suitable for everyone. There are also risks associated with the IVF process itself. It is important to discuss these risks in detail with your genetic counsellor or geneticist, or a specialist at a fertility clinic.

Your feelings

Having FAP or being at risk of it can be very difficult to cope with. There is the uncertainty of not knowing whether FAP could develop into cancer. There are often complicated decisions to be made about the right time to have surgery. Some people choose to have screening for longer because they find the thought of an operation very difficult. Others may choose to have surgery earlier because they find waiting for each screening hard. Talk to your doctor or nurse about any concerns you have.

FAP may affect you at a time when you are already coping with changes like puberty. It is often at a time when you are trying to become more independent. All these things can cause different issues and affect your relationships.

You may have many different emotions including anger, resentment, guilt, anxiety and fear. These are all normal reactions, and are part of the process many people go through in trying to come to terms with their condition. We have more information about the emotional effects of cancer.

Everyone has their own way of coping with difficult situations. Some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is there if you need it. Our cancer support specialists can give you information about counselling in your area.

Useful organisations

The Polyposis Registry

The Polyposis Registry is the UKs only specialist centre for patients with a polyposis syndrome. The nurse practitioners run an advice line for anyone with a polyposis syndrome – you do not have to be one of their patients. It is based at St Mark’s Hospital, Harrow.

IA (the ileostomy and internal pouch support group)

IA gives support and information for anyone who has had their colon removed.

FAP Gene Support Group

FAP Gene Support Group gives information about FAP.


PolyPeople is a support group for people with polyposis syndromes.

In addition to these, we have a list of organisations that may be able to offer you support and information. Our database lists useful organisations that provide both practical and emotional support, including information on health, benefits and financial help.