Inherited cancers: bowel cancer

Bowel cancer is a common cancer. Most people with bowel cancer do not have a gene mutation running in their family. If you are worried about bowel cancer in your family, talk to your GP. If needed, they will refer you to a genetics specialist.

A small number of people inherit gene mutations that cause conditions such as Lynch syndrome (LS) or familial adenomatous polyposis (FAP). These conditions are diagnosed by genetic testing or by the pattern of cancer in your family. People with LS or FAP have a higher risk of developing bowel and some other types of cancer.

If you have a higher risk of bowel cancer, there are ways to reduce that risk. This may include:

  • screening tests to find and treat early signs of bowel cancer
  • being aware of the symptoms of bowel cancer
  • treatments such as surgery to remove areas of healthy bowel
  • lifestyle changes.

Your genetics specialist will explain any side effects or disadvantages of these. For example, some risk-reducing treatments can affect your ability to get pregnant.

About bowel cancer

Bowel cancer is the third most common cancer in the UK for men and for women. But only a small number of bowel cancers are clearly linked to inherited cancer genes. 19 out of every 20 people (95%) with bowel cancer do not have a gene mutation running in their family.


Understanding bowel cancer in your family

An inherited bowel cancer gene may be more likely if there is a pattern of cancer in your family. These are examples of patterns:

If you are worried about the pattern of cancer in your family, start by talking to your GP. If needed, they will refer you to a genetics specialist.


Inherited bowel cancer genes

There are two main conditions caused by inherited gene mutations that are linked to bowel cancer:

  • Lynch syndrome
  • familial adenomatous polyposis.

Lynch syndrome

Lynch syndrome (also called hereditary non-polyposis colorectal cancer, or HNPCC) can be caused by several different inherited gene mutations. People affected by Lynch syndrome have a higher risk of bowel cancer and some other types of cancer, including womb cancer.

Bowel cancer usually affects people over the age of 50. If you are diagnosed with bowel cancer before 50, there is a higher chance it may be caused by Lynch syndrome. Your doctors can test a sample of the bowel tumour for signs it was caused by Lynch syndrome. If the test shows a gene mutation is likely, you may have a genetic test to look for it.

Familial adenomatous polyposis (FAP)

FAP is caused by an inherited mutation in a gene called the APC gene. This condition causes hundreds or thousands of growths in the bowel. These growths are called polyps. They usually start to appear when a person is in their teens. If the polyps are not removed, one or more of them will almost certainly develop into cancer. Less often, FAP may also cause other types of cancer.

Other inherited bowel cancer genes

There are other rare inherited conditions that can increase the risk of bowel cancer. These include:

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

Genetic Alliance UK offers information and support about rare inherited conditions.


Managing a higher risk of bowel cancer

If your family history or genetic test shows you have a higher risk of bowel cancer, there are ways to reduce that risk. This may include:

  • bowel screening tests
  • being aware of the symptoms of bowel cancer
  • risk-reducing treatments
  • lifestyle changes.


Bowel screening tests

You may be offered a test called a colonoscopy. This checks for bowel cancer or polyps that may develop into bowel cancer. Your genetics specialist will explain whether you need this test, when you should start having it and how often.

A colonoscopy is done with a thin, flexible tube with a light and camera on the end (a colonoscope). Once you are lying on your side, the doctor or nurse gently passes the tube into your back passage and into the bowel.

A colonoscopy
A colonoscopy

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You may have a sedative before the test to help you relax. If you find the test uncomfortable or painful, you may be given Entonox®. This is a gas that can relieve pain. It is sometimes called gas and air. You breathe it in through a mouthpiece.

During the test, the doctor or nurse checks the lining of the bowel for polyps or abnormal areas. If there are small polyps, the doctor or nurse may remove these during the colonoscopy. They may also take small samples of any abnormal areas to test for cancer cells.

Surgery is often the most effective way to treat or prevent bowel cancer. Your doctor may talk to you about having surgery to remove an area of bowel if a colonoscopy finds:

  • changes that are very likely to develop into cancer
  • cancer cells.


Be bowel aware

When it is found early, bowel cancer can be treated very successfully. Try to be aware of changes that could be a sign of bowel cancer. See your GP if you have any of these symptoms:

  • Bleeding from the back passage (rectum) or blood in your poo.
  • Looser poo or diarrhoea that lasts for 3 weeks or more.
  • A feeling that your bowel is not properly empty after going to the toilet.
  • A pain or lump in the tummy or back passage.
  • Loss of weight or appetite.
  • Feeling more tired (fatigued) than usual for some time, with no obvious reason.

Bowel problems are very common, so these symptoms may not be caused by cancer. But if you have a higher risk of bowel cancer, it is important to get them checked.


Risk-reducing treatments and Lynch syndrome

If you have Lynch syndrome, you may be offered the following treatments: 

  • Aspirin – Taking aspirin tablets regularly may help prevent cancer in people affected by Lynch syndrome. More research is needed to know what the most helpful dose is. Aspirin can also have harmful side effects. 
  • Surgery to remove areas of healthy bowel – If you have surgery to remove a bowel cancer, you may also decide to have areas of healthy bowel removed. This reduces your risk of more bowel cancers developing in the future.
  • Surgery to remove the womb and ovaries – Women with Lynch syndrome may choose to have this surgery. It reduces the risk of womb and ovarian cancer. After the surgery, you will start the menopause if you have not already. This means you will no longer be able to get pregnant. 

It is important to talk to your doctor about the side effects, risks and benefits of any treatment you are offered. If you have questions about fertility, you can ask to see a fertility specialist for further advice. If a treatment causes an early menopause, there are treatments that can help manage any symptoms.


Risk-reducing treatments and FAP

For people affected by FAP, the only effective way to prevent bowel cancer is surgery to remove the large bowel. Most people choose to have bowel screening in the early stages for a while, before they have surgery. When the number of polyps increases, this may be a sign that surgery is needed.

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. It is important to talk to your doctor about the side effects, risks and benefits of surgery before you make a decision.


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