Colorectal Cancer—Patient FAQ

Colorectal cancer (CRC) is a cancer of either the colon (large intestine) or the rectum. It is the second-most common cause of cancer death in men and the third-most common cause in women. It often starts as a polyp (abnormal growth) in your colon or rectum that grows into cancer. Some people may have CRC without being aware that they have it, so it is helpful to get tested. One common sign of CRC is blood in the stool.

Please note that the recommendations do not apply to people with previous CRC or polyps, inflammatory bowel disease (e.g., colitis or Crohn’s disease), signs or symptoms of CRC, history of CRC in one or more of your first-degree family members, or some inherited conditions (such as Lynch syndrome and familial adenomatous polyposis).

Discuss colorectal cancer screening with your primary care provider, and weigh the benefits and harms of each test.

1. When should I get screened for colorectal cancer (CRC)?

  • If you are between the ages of 50 and 74, we recommend that you speak to your primary care practitioner about screening.

2. Why should I not get screened if I am under the age of 50 or over the age of 74?

  • There is no benefit in screening those younger than 50 as the number of new cases of CRC in this age group is very low.
  • There is not enough evidence to show a benefit of screening those older than 75. However, if you still wish to be screened, we recommend that you speak to your primary care provider.

3. What tests are used to screen for CRC and how often should they be done?

  • There are two types of tests we recommend: a fecal occult blood test (FOBT) or a flexible sigmoidoscopy.
    • An FOBT is the most common test, and will most likely be the first choice. To do an FOBT, you provide a stool sample that is tested for blood that can’t be seen with the naked eye. Blood in the stool can be a sign of CRC.
    • Flexible sigmoidoscopy is less commonly used and requires more resources. It is a procedure that involves inserting a long flexible tube with a light and a camera attached to it into the anus, rectum, and lower colon to look for polyps. Before the procedure, you will need to cleanse your bowel with enemas or laxatives.

4. How often should I be screened?

  • If you and your primary care provider choose the FOBT, we recommend screening with this test every 2 years.
  • If you and your primary care provider choose flexible sigmoidoscopy, we recommend screening with this test every 10 years.

5. Are there any harms associated with these tests?

  • The primary harms of FOBT are false positives and false negatives
    • A false positive result occurs when a test says that someone may have CRC when they actually do not. This can lead to unnecessary further testing, such as a colonoscopy and its related harms.
    • A false negative result occurs when a test says that someone does not have CRC when they actually do.
  • Harms for flexible sigmoidoscopy are rare and occur in less than 0.1% of patients. These harms include intestinal puncture, minor bleeding, major bleeding, and death.

6. Which test is best for me?

  • If you would prefer to have a less invasive procedure and don’t mind getting tested more frequently, the FOBT might be best for you.
  • If you would prefer less frequent testing and don’t mind having a more invasive test, flexible sigmoidoscopy might be the preferred option, if it is available in your location.
  • Remember to check with your primary care provider about the availability of each test in your region. An FOBT is more readily available and therefore the majority of people will be screened with this test.

7. Should I be screened for CRC with a colonoscopy?

  • We recommend not using colonoscopy as a routine screening test for CRC. There are several reasons for this:
    • There isn’t enough evidence that having a colonoscopy is more helpful than other available tests.
    • This test has a slightly greater risk for harm than flexible sigmoidoscopy.
    • Wait lists for colonoscopy are very long in Canada and have increased over time because the test requires specialized equipment and trained clinicians to perform it.

8. What is the difference between colonoscopy and flexible sigmoidoscopy?

A colonoscopy lets a doctor look at the lining of the entire rectum and colon, whereas flexible sigmoidoscopy examines only the rectum and lower third of the colon.