Patient information from BMJ

Colon cancer: should I be screened?

Last published:Jul 24, 2020

Colon and rectal cancer (sometimes called colorectal cancer) is a serious condition, but it can often be cured if it's caught early. To pick up early signs of the disease, doctors recommend people have screening tests as they get older, or if they have an increased chance of getting this cancer.

What is colon and rectal cancer?

Cancer of the colon or rectum is cancer that starts in your large intestine.

Your large intestine turns food your body doesn't need into solid waste. The waste then leaves your body when you go to the bathroom. The upper part of your large intestine is called the colon and the lower part is called the rectum.

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

Colon and rectal cancer is one of the main causes of death from cancer in the United States.

What is colon and rectal cancer screening?

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

Doctors use several different tests to screen for colon and rectal cancer. These are the most common.

• Fecal 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 tumor in your colon or rectum. A newer version of this is the fecal immunochemical test (FIT).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, they can take a sample of tissue to look at more closely.

  Just before the test, you will probably be given a medication 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 intestine. It is also sometimes called a virtual colonoscopy.

For a colonoscopy or a virtual colonoscopy, you'll need to empty your colon and rectum 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 intestine 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 intestine with water through a tube.

Should I be screened?

In the United States, regular screening for colon and rectal cancer is recommended for most men and women over age 50. However, doctors recommend that people who are at high risk of colon and rectal cancer get tested earlier and more often.

Most men and women are advised to follow one of these testing plans from age 50 to 75:

• A fecal occult blood test (FOBT) or a fecal immunochemical test (FIT) every year

• Flexible sigmoidoscopy every five years, along with a FOBT every three years

• Colonoscopy every 10 years (doctors often recommend this approach).

The screening plans above are for men and women who have an average risk of getting colon and rectal cancer. This means they have no health problems or family history that puts them at higher risk of this cancer.

People who have an increased chance of colon and rectal cancer can be tested earlier and more often. Things that increase your risk include:

• having previously had colon or rectal cancer, or polyps.

  Colon and rectal 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 in the past, or you've had colon or rectal cancer before, you'll need more frequent screening.

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

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

• having an inherited condition that increases your chance of colon and rectal 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 colon or rectal cancer. These include:

• a change in your bowel movements that lasts for several weeks. This could be loose stools and needing to go to the bathroom 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 colon or rectal 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 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, 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 specializes in colon and rectal cancer. The doctor will need to do some further tests to plan the best treatment for you.

The main treatments for colon and rectal cancer are surgery, radiation therapy, and treatment with anticancer drugs (chemotherapy). To learn more, see our leaflet Colon and rectal cancer: what is it? and Colon and rectal cancer: what treatments work?

Where to get more help

You can find out more about colon and rectal cancer screening by talking with your doctor. Screening resources are also available on the web. For example, you can find detailed information on the Centers for Disease Control and Prevention (CDC) website at cdc.gov.