Familial Adenomatous Polyposis

What is FAP?

FAP is a condition that runs in families. Conditions that run in families may be referred to as inherited or familial. People with FAP have an increased risk of getting cancer of the bowel. About 1 in every 100 of all bowel cancers are linked to FAP.

People with FAP have hundreds or thousands of small growths called polyps in the bowel. These are also sometimes called adenomas. This is where the adenomatosis part of FAP comes from and polyposis just means lots of polyps.

FAP can also affect people who don’t have a history of it within their family. This happens in about 1 in 3 people with FAP.

The polyps usually start to appear when you are in your teens. And if they aren’t treated one or more of them will almost certainly develop into cancer (usually by the age of 40). There’s a type of FAP called attenuated FAP in which the polyps appear about ten years later than with the usual FAP.
Most people with FAP are offered the choice of having an operation to remove the bowel when they’re young. This can be hard to cope with but it means that you can avoid getting bowel cancer.

Does FAP affect any other parts of the body?

FAP can have some effects on other parts of the body. Most people have some harmless changes (like black dots) at the back of the eye (retina). They don’t affect your vision at all and often help to diagnose FAP. Some people get harmless lumps which affect the bones or cysts on the skin.
You can also get polyps in the stomach. These are usually harmless but they will need to be checked regularly. There’s also a very slightly increased risk of getting cancer in other parts of the body (duodenum|, thyroid, adrenal and pancreas). The risk is greatest for cancer of the small bowel (duodenum), but it’s still very low. You may have regular tests to check for this.

People with FAP also have a higher risk of developing a rare tumour called a desmoid tumour. It develops and grows in the fibrous tissue that covers muscle and other organs. It’s not a cancer and doesn’t spread to other parts of the body.

The large bowel

The bowel is part of our digestive system. It’s 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. This is where the body absorbs 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 bowel, which goes up, is called the ascending colon. It then goes across to the left side of the abdomen (the transverse colon). After this, it goes down to the bottom of the abdomen (the descending colon) and ends in the sigmoid colon, the rectum and the anus.

How is it inherited?

FAP is caused by a fault in a gene called the APC gene. Our genes carry the information that’s 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 that they have a healthy gene but also one that’s faulty.

If that person has a child there is a fifty-fifty chance that they will pass on the faulty gene (only one copy of a gene is passed on from each parent). If a child has inherited the faulty gene they will develop FAP.
In about 1 in 3 people a faulty APC gene happens with no history of FAP in the family. Their children will still have a fifty-fifty chance of inheriting the faulty gene.

Treatment for FAP

If the person is very young or the polyps look harmless they may continue with regular bowel checks for a while. But once there are lots of polyps in the bowel it’s impossible to know when one of these could become a cancer. So an operation is the safest way to treat FAP and prevent bowel cancer.

Surgery

• 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 can go to the toilet normally but more often than before. There is still a risk that polyps may develop in the rectum so you will need a test to check this every year.

• Removing the colon and the rectum Sometimes the lining of the rectum is removed to avoid the risk of polyps developing. 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 can go to the toilet normally but usually more often than before. You might need to take antidiarrhoea medicine. Tests on the rectum won’t be needed because the lining (where polyps grow) has been removed.

• Having a stoma Some people need to have the rectum removed. The end of the small bowel is brought out onto 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.

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