Screening for colorectal cancer

Screening for colorectal cancer is easy and convenient. All you need to do is have a stool test once you turn 50 – and keep having one every two years.

A stool test might be something you’d rather avoid. But it could save your life – it’s that simple. Colorectal cancer responds best to treatment when it is found and treated as early as possible. Treatment is most effective before the disease spreads outside of the colon.

Our colorectal cancer screening recommendations

The Canadian Cancer Society recommends that men and women age 50 and over have a stool test (guaiac-based fecal occult blood test or fecal immunochemical test) at least every 2 years. There is convincing evidence that stool tests with appropriate follow-up can significantly reduce deaths from colorectal cancer.

Follow-up for a positive test should include a colonoscopy or double contrast barium enema (an x-ray of the large intestine) or flexible sigmoidoscopy.

This recommendation applies only to people who are at average risk of developing colorectal cancer. People who have a first-degree relative with colorectal cancer, personal history of colorectal cancer, inflammatory bowel disease, some inherited syndromes or benign polyps should develop an individualized plan of surveillance with their doctors.

Colorectal cancer screening programs should ensure that:

people are given information about the risks and benefits of the screening tests
the impact of positive test results are explained
people whose stool tests are positive are referred for definitive diagnostic testing in a timely manner
a database is created to ensure that candidates for tests and their physicians are notified when testing is recommended, and to enable the results of the colorectal cancer screening program to be analyzed and reported
the most effective technology should be used

Tests for colorectal cancer

Polyps or tumours in the colon have blood vessels that can release a small amount of blood onto the stool when it passes by. Stool tests check for this occult (hidden) blood that you can’t see with your eyes.

Two types of stool tests are used in Canada to screen for colorectal cancer.

Guaiac-based fecal occult blood test (gFOBT)

Uses a chemical reaction on a paper card to find traces of blood in the stool.

Fecal immunochemical test (FIT)

Uses specific antibodies to find traces of blood in the stool.

For both types of test, you collect the stool samples at home and place them on a stool collection card or in a stool collection container. Depending on where you live, you then take or mail the samples to a medical laboratory. Certain foods and drugs can affect some stool tests, so be sure to check the instructions that come with the test kit. Ask your doctor if you have any questions.

Colorectal cancer screening programs vary among the provinces and territories, so ask your doctor about how the program works where you live.

If there is blood in the stool

If a stool test shows traces of blood in your stool, you will need to have more tests to find out where the bleeding is coming from and why. Your doctor may suggest:

Colonoscopy – a thin, flexible tube with a light and camera at the end is used to look at the lining of the entire colon. Watch a colonoscopy.
Flexible sigmoidoscopy – a soft, bendable tube with a light and camera at the end is used to look at the lining of the rectum and the lower part of the colon.
Double-contrast barium enema – an x-ray of the colon and rectum that uses a special dye (called barium). The dye helps show the lining of the colon more clearly.

If the tests show something abnormal, tissue samples for further testing (a biopsy) may be taken during a colonoscopy or sigmoidoscopy.

Other reasons for having blood in the stool

Having blood in your stool doesn’t always mean that you have polyps or cancer. Blood may come from the colon or from other parts of the digestive tract, such as the stomach or anus. The bleeding can be caused by:

ulcers (sores on the lining of your digestive tract)
hemorrhoids (enlarged or swollen veins of the anus and rectum)
diverticulosis (tiny pouches that form at weak spots in the colon wall)
ulcerative colitis or Crohn’s disease (inflammation of the colon, also often called inflammatory bowel disease)

Benefits and risks of screening for colorectal cancer

Almost every test or procedure has benefits and risks. It’s important to be aware of them so that you can make an informed decision that’s right for you. No screening test is 100% accurate, but the scientific evidence tells us that having stool tests leads to a decrease in death rates in people with cancer.

Benefits

Better survival rates – In most cases, the earlier a cancer is detected (found), the better your chance of survival. Research has shown that people who have regular stool tests are more likely to survive colorectal cancer. Stool tests check for hidden (occult) blood found in the stool. Polyps or tumours in the colon have blood vessels on their surface that can release a small amount of blood in the stool. Stool tests can prevent cancer by detecting polyps that can be removed before they become cancerous.
Better quality of life – Early detection may also mean less treatment and less time spent recovering.

Risks

False-positive results – This happens when test results suggest cancer even though cancer is not present. False positives can cause anxiety, stress and possibly painful and unnecessary tests to rule out cancer (that is, to make sure you don’t have cancer when the screening test has suggested you might).
False-negative results – This happens when cancer is not detected by the test even though it is present. False negative results can cause you or your physician to ignore other symptoms that suggest the presence of cancer, causing a delay in diagnosis and treatment.
Overdiagnosis – Certain cancers may never cause any symptoms or decrease life expectancy or quality of life. However, research shows that most colorectal cancers are harmful and that colorectal cancer should be detected and treated as early as possible.
Increased exposure to harmful procedures – A colonoscopy may be needed after a positive stool test. There can be risks with this procedure such as bleeding and bowel perforation.