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The advisory, from the Canadian Task Force on Preventive Health Care, says that low-risk, symptom-free adults aged 50 to 74 should instead be screened with a fecal occult blood test (a stool-based screen) every two years, or a procedure known as flexible sigmoidoscopy every 10 years.
Flexible sigmoidoscopy involves the use of a flexible scope to examine the lower portion of the colon and rectum, rather than the entire tract.
The guideline is somewhat similar to the guideline of the U.S. Preventive Services Task Force to screen adults aged 50 to 75 with fecal occult blood tests, flexible sigmoidoscopy or colonoscopy.
But, while the U.S. recommendations include colonoscopy, the Canadian task force does not believe there is enough evidence to do so.
Two experts in the United States reaffirmed their support of colonoscopy.
"There is strong literature supporting the benefit of colonoscopy in the appropriately selected patient," said Dr. Jules Garbus, a colorectal surgeon at Winthrop-University Hospital in Mineola, N.Y.
Dr. David Bernstein is chief of hepatology at Northwell Health in Manhasset, N.Y. He noted that "colonoscopy every 10 years to screen for colon cancer in asymptomatic low-risk adults [age 50 and over] is the current recommendation of the American College of Gastroenterology, the American Gastrointestinal Association, American Society of Gastrointestinal Endoscopy, the American Cancer Society and the U.S. Preventive Services Task Force."
According to Bernstein, "colonoscopy remains the only diagnostic and therapeutic modality which has been shown not only to diagnose cancer but to prevent cancer as well."
The new Canadian guideline, published Feb. 22 in the Canadian Medical Association Journal, changes the prior guideline from the panel, which recommended a fecal occult blood test every year or two years and flexible sigmoidoscopy every five years in adults with no symptoms.
Dr. Maria Bacchus is chair of the Canadian guideline working group and a general internist at the University of Calgary, Alberta. In a journal news release, she explained the panel's decision.
"Although colonoscopy may offer clinical benefits that are similar to or greater than those associated with flexible sigmoidoscopy, direct evidence of its efficacy from randomized controlled trials in comparison to the other screening tests ... is presently lacking," she said. "However, ongoing clinical trials are working to address this research gap."
According to the new Canadian guideline, "although flexible sigmoidoscopy is not frequently performed for screening in many jurisdictions, it may warrant further consideration because it can be completed in the same facilities as colonoscopy and using similar equipment, but without the requirement of a specialist, such as a gastroenterologist."
Also, "waitlists for colonoscopy remain long in Canada and have increased over the years," Bacchus noted.
Both Garbus and Bernstein agreed that the structure of the Canadian medical system may be playing a role in the panel's decision to curb the use of colonoscopy.
"In Canada's socialized system of medicine, resources are quite limited leading to long waiting times for patients to receive the health care that they require," Garbus said. "This may account for the Canadian guidelines being similar to the U.S. Preventative Services Task Force recommendations, but lacking the colonoscopy component."
And Bernstein said that the Canadian group's guideline "seem to be based more on access to care and cost control rather than good medical care."
The new Canadian guideline also advises that people 75 and older should not be screened for colon cancer if they have no symptoms, and that doctors should discuss screening with patients aged 50 to 59 due to the lower incidence of colon cancer in this age group.
Doctors should also discuss colon cancer screening with people older than 75 because of their shorter life expectancy and the lack of evidence about possible benefits or harm, according to the Canadian guideline.
-- Robert Preidt
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SOURCES: Jules Garbus, M.D., colorectal surgeon, Winthrop-University Hospital, Mineola, N.Y.; David Bernstein, M.D., chief, division of hepatology, Northwell Health, Manhasset, N.Y.; Canadian Medical Association Journal, news release, Feb. 22, 2016