Screening for colorectal cancer—that is, cancers of the colon (large intestine) and rectum—is a proven lifesaver. This is partly due to the fact that this is one cancer which screening can actually prevent, since it can lead to the detection and removal of polyps, some of which may progress to cancer.
So why are anywhere from one-third to one-half of Americans over 50 not getting the recommended tests for colorectal cancer? One reason this screening rate lags behind those for some other cancers may be an overemphasis on colonoscopy as the screening test of choice in this country.
For years many experts, organizations and media spokespeople such as Katie Couric have promoted colonoscopy as the best colorectal screening test. As a result, it has become the most frequently used screening test for colorectal cancer in the U.S. Most doctors today do not even discuss alternatives with their patients.
Offering only colonoscopies discourages some people from getting tested, since they may dread the bowel-cleansing prep (clear liquid diet, strong laxatives and high fluid intake), are scared or embarrassed about the procedure itself, worry about potential complications and/or can’t afford its high price. Medicare and private insurance cover colonoscopy and other screening tests, but that leaves out uninsured people, who are only half as likely to be screened for colorectal cancer as the insured.
Colonoscopy is a good test, though not perfect. You should know your other screening options as well. “Much more screening will be carried out if primary care providers and the American public are not made to feel that screening tests other than colonoscopy are ineffective,” says James Allison, M.D., professor emeritus of medicine at the University of California, San Francisco, and a leading expert on colorectal cancer screening.
Colonoscopy: strengths and weaknesses
Colonoscopy examines the colon via a flexible scope that transmits the images to a video screen while the patient is sedated. The claim that it is the best screening option has been based on assumptions and expectations about what it can do—allow a doctor to examine the entire colon and rectum and remove polyps during the procedure.
But colonoscopy’s superiority has never been proven in randomized controlled trials (the “gold standard”) comparing its effectiveness to other tests.
Other kinds of studies have suggested that colonoscopy (typically done every 10 years if no cancer or polyps are found) doesn’t save more lives than sigmoidoscopy, which examines only the lower part of the colon and is usually done every five years. In some studies, sigmoidoscopy was combined with stool tests. Two large randomized controlled studies comparing colonoscopy with stool tests are underway, but results won’t be available for years.