3 common questions about colon cancer screening

Colorectal cancer is the third most commonly diagnosed cancer in Canada. We'll answer some of the most common questions people have about this disease and its screening procedures.

Remember that a colonoscopy is the gold standard for a reason. A colonoscopy allows a doctor to view the entire large intestine, making it the best method for detecting colon tumours and polyps (small wart-like growths on the lining of the intestine that may turn cancerous).

• Studies show that colonoscopies detect about 90 per cent of large polyps and 75 per cent of smaller ones. The detection rate for full-blown colon cancer is even higher.
• A sigmoidoscopy examines only the lower portion of the large intestine (called the sigmoid or descending colon) and the rectum.
• The test is cheaper and faster than a colonoscopy, doesn't require sedation and carries a lower risk of complications. The downside? It can't see tumours and polyps in approximately half of the colon.
• Here's the bottom line: a colonoscopy is considered by most doctors to be the first line of defense against colon cancer. But if you can't get one for some reason, a sigmoidoscopy with annual fecal occult blood testing is your next best bet.

Virtual colonoscopy is a tempting alternative, but more research is needed before experts can recommend it in place of a traditional colonoscopy.

• Virtual colonoscopy produces three-dimensional images of your colon with no sedation required. The procedure is over in about 10 minutes, which is much faster than conventional colonoscopy.
• Though it sounds great, there are drawbacks. Virtual colonoscopy doesn't excuse you from the pre-test bowel cleansing ritual that no one enjoys, and if the test finds a polyp, you'll need to follow up with a traditional colonoscopy (and repeat the bowel cleansing ritual) to have the polyp removed.
• A virtual colonoscopy's accuracy may depend on who's performing the test. Virtual colonoscopy is still a new screening test, and several reports suggest that many doctors haven't quite mastered it yet.

The fecal occult blood test (FOBT) is a relatively simple test that can detect traces of blood in the stool, which is often the only symptom of colorectal cancer.

• A single FOBT isn't as accurate as a colonoscopy, though having one annually increases its effectiveness. It may be worthwhile between sigmoidoscopies, or as a bare-minimum screening method if you can't or won't have a sigmoidoscopy or colonoscopy.
• Blood in the stool may be a sign of cancer, or it may be evidence that you have polyps (small growths that can turn into tumours). However, a positive test doesn't necessarily mean that you have colorectal cancer. A number of gastrointestinal problems can produce blood in the stool, including colitis, hemorrhoids, Crohn's disease, and others.
• If an FOBT finds blood in your stool, your doctor will order further tests to determine the cause.

Because of how common and severe colorectal cancer is, it's important to take testing seriously. Be sure that you speak with your doctor and consider all of the possible testing options to find the right one for you. And remember: when it comes to colon cancer, you can't be too careful.