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New Canadian guidelines state there is not enough evidence to justify colonoscopies as routine screening for colorectal cancer. Instead, patients should undergo fecal occult blood testing every two years, or flexible sigmoidoscopy – a procedure in which a scope is inserted in the lower portion of the colon and rectum rather than the entire tract – every 10 years.

The guidelines, published on Monday in the Canadian Medical Association Journal, apply to adults aged 50 to 74 who are asymptomatic and at low risk for colorectcal cancer, meaning they have no prior history of the disease, no family history, symptoms such as blood in the stool, or genetic predisposition. The last time the guidelines were updated was 2001, and the new recommendations are meant to reflect the "major changes in technology and practice" that have occurred since then, the authors wrote.

"We have a lot more evidence to give, information around screening intervals [and] when to start and stop screening," said Dr. Maria Bacchus, chair of the Canadian Task Force on Preventive Health Care working group on colorectcal cancer and internist at Calgary's Foothills Medical Centre. The task force is an independent body of 14 primary care and prevention experts who develop clinical practice guidelines.

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Colorectal cancer is the third most commonly diagnosed cancer in Canada. It is the second leading cause of cancer death in men and the third in women.

Every province has an organized screening program or is implementing one. The territories do not. Nunavut has plans to develop one. Bacchus said she hopes the guidelines will push everyone to get on board.

Currently, no provincial screening program includes flexible sigmoidoscopy, and the guideline authors suggest policy-makers may want to consider the benefits as well as the cost of both screening methods before making a decision.

Ultimately, most Canadians will likely be screened using fecal occult blood tests, which look for microscopic specks of blood in the stool that could be a sign of cancer, Bacchus said. If blood is found, most provincial programs recommend colonoscopies as a follow-up test to determine whether a person has colorectal cancer.

Amy Elmaleh, executive director of the advocacy group Colon Cancer Canada, said while the guidelines are important, what is also needed is more education and awareness about the risks of the disease and the importance of regular screenings.

"You want there to be less stigma. It's a challenge," she said.

Technological developments in recent years improved both fecal occult blood testing and sigmoidoscopies.

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Many gaps in the research still need to be closed, Bacchus said. For instance, the guidelines recommend against routine screening of adults with no symptoms who are older than 74. However, the recommendation is based on weak and low-quality evidence of the effectiveness of colorectal screening in that age group. So the authors suggest that adults 75 and over who are in good health may want to discuss their options with their doctor.

Some questions are also unanswered about whether colonoscopies are more effective than fecal occult blood tests or other screening methods. But because waiting lists are long and the potential for side effects such as bleeding or intestinal perforation are greater than they are for other tests, the guidelines recommend against using colonoscopies as a routine screening tool in asymptomatic low-risk adults.

The U.S. Preventive Services Task Force, on the other hand, continues to recommend colonoscopies for primary screening, as well as fecal occult blood testing and flexible sigmoidoscopy.

Dr. Jennifer Telford, medical director of the BC Cancer Agency's colon screening program, said Canada's guidelines make the most sense. People who are in good health are much more likely to do a non-invasive stool test than a colonoscopy, which increases the likelihood more people will get screened.

"I think [colonoscopy] is a great test, but in terms of population-based colon cancer screening, I don't think that is the right test," Telford said.

She added that large studies are under way to evaluate how well fecal tests work compared to colonoscopies. Those results could help shape future recommendations.

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