Patient information from BMJ

Bowel cancer: should I be screened?

Last published:Jul 24, 2020

Bowel cancer is a serious disease, but it can often be cured if it's caught early. To pick up early signs of bowel cancer, doctors recommend people have screening tests as they get older or if they have a raised risk of bowel cancer.

What is bowel cancer?

Bowel cancer is one of the main causes of death from cancer in developed countries.

The cancer starts when some cells in the inside wall of the large bowel start dividing too fast. Treatment aims to remove or kill the cancer cells and stop them spreading to other parts of your body.

The term 'bowel cancer' includes cancers of the colon and rectum, which make up the upper and lower part of your large bowel. Bowel cancer is sometimes called colorectal cancer.

Your large bowel turns food your body doesn't need into solid waste. The waste then leaves your body when you go to the toilet.

What is bowel cancer screening?

Bowel cancer screening involves looking for signs of cancer in healthy people. The aim is to spot cancer before it starts causing problems, so treatment can be started straight away.

Several different tests can be used for bowel cancer screening. Different countries have different screening recommendations. So what tests you'll be offered, and at what age, depends on where you live. However, these are the most common tests.

• Faecal occult blood test (FOBT). A sample of your stool is tested for blood. If you have blood in your stool, it might be because you have a tumour in your colon or rectum. A newer version of this is the faecal immunochemical test (FIT). This test looks for a particular type of blood that is more likely to mean cancer.

• Flexible sigmoidoscopy. A doctor puts a thin, bendy tube into your anus. This allows the doctor to look at your rectum and the lower part of your colon.

• Colonoscopy. A doctor puts a thin, bendy tube into your anus. This is pushed up your colon so the doctor can see all the way along it.

  If your doctor sees anything unusual during the test, he or she can take a sample of tissue to look at more closely.

  Just before the test, you will probably be given a medicine to make you sleepy (a sedative). This is to make the test less uncomfortable. Colonoscopy is also used as a follow-up test if your doctor finds any possible problems during one of the other screening tests.

You might also be offered a test called a computed tomography colography. This test uses a computer to put together scans to build up a picture of the inside of your bowel. It is also sometimes called a virtual colonoscopy.

For a colonoscopy or a virtual colonoscopy, you'll need to empty your whole bowel before the test. So you'll take a laxative the day before, and you won't be able to eat or drink anything on the day of the test.

You also can't eat solid food for a while before a colonoscopy - your doctor will give you detailed instructions.

If you have a flexible sigmoidoscopy, only the lower part of your bowel needs to be emptied. You may have a laxative before the test, or have an enema, which involves washing out the lower part of your bowel with water through a tube.

Should I be screened?

The age when people start screening for bowel cancer varies from country to country.

In England, for example, men and women aged 60 to 74 are invited to have screening with a faecal occult blood test (FOBT) every two years. They are also invited to have a one-time flexible sigmoidoscopy at age 55.

These screening programmes are for people who have an average risk of getting bowel cancer. This means they have no health problems or family history that puts them at higher risk of this cancer.

People who have a raised risk of bowel cancer can get tested earlier and more often. Things that increase your risk of bowel cancer include:

• having had previous polyps or bowel cancer. Bowel cancer usually starts in small growths called polyps. Adenomatous polyps are a type that is particularly likely to develop into cancer.

  If you've had adenomatous polyps removed from your bowel in the past, or you've had bowel cancer before, you'll need more frequent screening.

• a family history of bowel cancer. This means that a close relative (a parent, child, brother, or sister) had bowel cancer or adenomatous polyps before age 60, or two close relatives had bowel cancer at any age.

• having ulcerative colitis or Crohn's disease. These are long-term diseases that cause inflammation (swelling and irritation) inside the bowel. This increases your risk of bowel cancer.

• having an inherited condition that increases the chance of bowel cancer. These include familial adenomatous polyposis (FAP), Lynch syndrome, and MYH-associated polyposis (MAP).

  These are rare diseases that run in families. If your doctor suspects you may have one of these conditions, you can have genetic testing to find out for certain.

What will happen after my test?

If you have a negative result

A negative result means the test did not find any signs of cancer. This is reassuring. But remember that no test is 100 percent accurate.

You should still see your doctor if you have any symptoms that could mean bowel cancer. These include:

• a change in your bowel habits that lasts for several weeks. This could be loose stools and needing to go to the toilet more often, or bad constipation

• repeated bleeding from your anus

• visible blood in your stools

• bad pain in your abdomen.

If you have a positive result

A positive result can make you feel anxious. But a positive result with most screening tests doesn't mean you definitely have cancer. A colonoscopy is the only test that can tell you for certain whether you have bowel cancer.

You'll be sent for a colonoscopy if you get a positive result from any of the other screening tests. Colonoscopy is a very thorough test for bowel cancer, because it can see the full length of the colon and rectum.

If the colonoscopy finds any polyps, these can be removed during the colonoscopy.

If the colonoscopy finds any abnormal-looking areas in the bowel, the doctor will also remove a small piece of tissue during the test. Doctors call this taking a biopsy.

Any removed tissue or polyps are then examined for cancer cells.

If cancer cells are found, you will be referred to a doctor who specialises in bowel cancer. The doctor will need to do some further tests to plan the best treatment for you.

The main treatments for bowel cancer are surgery, radiotherapy, and treatment with anticancer drugs (chemotherapy). To learn more, see our leaflets Bowel cancer: what is it? and Bowel cancer: what treatments work?

Where to get more help

You can find out about screening programmes and recommendations in your country by talking with your doctor. Resources are also available on the web.

For example, you can find detailed information about the UK bowel cancer screening programme at nhs.uk/conditions/bowel-cancer-screening/.