Screening for colorectal cancer

When colorectal cancer is detected and treated early, the chances of successful treatment are better. Screening tests help find colorectal cancer before any symptoms develop. Screening means checking or testing for disease in a group of people who don’t show any symptoms of the disease.

Currently, the most reliable method of finding colorectal cancer early is testing the stool for occult (hidden) blood.

People should talk to their doctor to learn more about their personal risk of colorectal cancer and to take advantage of screening tests or programs.

Currently, screening for colorectal cancer with stool tests, either the fecal occult blood test (FOBT) or fecal immunochemical test (FIT), is recommended in Canada at least every 2 years for people age 50 and over.

More about fecal occult blood test (FOBT) and fecal immunochemical test (FIT)

An FOBT checks for hidden (occult) blood in the stool. Polyps or tumours in the colon have blood vessels on their surface that can release a small amount of blood into the stool. FOBT helps identify adenomatous polyps early, before they become cancerous.

There are 2 types of FOBT used to screen for colorectal cancer in Canada:

• guaiac-based FOBT – This is the most common type of FOBT. Guaiac-based FOBT uses a chemical reaction on a paper card to find traces of blood in the stool from adenomatous polyps or tumours.
• FIT (or iFOBT) – This is a newer type of FOBT that uses specific antibodies for human blood to find traces of blood in the stool. FIT is being used by some, but not all, screening programs in Canada.

There may be diet or drug restrictions with some FOBT kits. It is important to check the instructions included in the test kit. Your doctor may give you a list of food and drugs to avoid before taking the test.

For FOBT, a person collects stool samples from 2–3 separate bowel movements in their own home. These samples are placed on a special stool collection card. The person then either takes the stool collection cards to a medical laboratory for testing or mails the samples back in a postage-paid envelope, if one is provided.

A negative FOBT result means that blood has not been found in the stool. A positive result means that blood has been found in the stool. People who have a positive result will need to have further testing.

High-risk individuals

People who are at higher than average risk of developing colorectal cancer may need to be tested more often and at an earlier age than people with average risk. Examples of what puts a person at higher than average risk include:

• a first-degree relative (parent, sibling or child) with colorectal cancer
• a personal history of colorectal cancer
• a personal history of benign polyps in the colon or rectum
• inflammatory bowel disease (ulcerative colitis or Crohn’s disease)
• inherited conditions, such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (HNPCC)

People who are at higher than average risk should talk to their doctor about a personal plan for testing. A personal plan for testing may include:

• FOBT (guaiac-based FOBT or FIT)
• genetic risk assessment, counselling and testing, if available
• colonoscopy – a test that lets the doctor look at the lining of the entire colon using a long, thin, lighted tube
• flexible sigmoidoscopy – a test that lets the doctor look at the lining of the rectum and lower part of the colon using a thin, flexible tube
• double-contrast barium enema – an x-ray of the colon and rectum

Follow-up

If an FOBT shows that there is occult blood in the stool, follow-up tests may be done. They include:

• colonoscopy
• flexible sigmoidoscopy
• double-contrast barium enema

Screening programs

Many provinces have organized screening programs for colorectal cancer.

See a list of questions to ask your doctor about screening.