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The findings could make doctors rethink whether the less invasive, five-minute sigmoidoscopy of the lower bowel plus the fecal blood test could be better than a colonoscopy. ((Jean-Paul Pelissier/Reuters))

A one-time scope test to detect signs of colorectal cancer could save hundreds of thousands of lives worldwide each year, according to the world's largest and longest running study.

Colorectal cancer is the third-most frequently diagnosed cancer worldwide, accounting for more than one million cases and 600,000 deaths every year, including 8,900 deaths in Canada.

The study in Wednesday's online issue of the medical journal the Lancet is the first to definitely state that detecting and removing precancerous growths called polyps can reduce colorectal cancer incidence and deaths.

The researchers followed more than 170,000 healthy volunteers aged 55 to 64 who were followed for an average of 11 years. Of those, 40,674 had a one-time "flexi-scope" or flexible sigmoidoscopy screening test — an exam that removes polyps, small growths that could become cancerous.

Their colon cancer results were compared with 113,195 healthy volunteers aged 55 to 64 people who were not screened.

After 11 years of followup, colorectal cancer incidence was reduced by a third, and colorectal cancer mortality was reduced by 43 per cent, the researchers found.

"It's not for me to tell governments what to do," said Dr. Wendy Atkin, a professor of surgery and cancer at Imperial College London, who led the research. "But this is a very big effect, with a very quick and a very cheap test."

Canadian changes?

The test only needs to be done once for people in their 50s, Atkin said. Since sigmoidoscopy only works on the lower bowel, other exams such as the fecal blood test would still be needed.

"The results from our trial show that flexible sigmoidoscopy is a safe and practical test and, when offered only once to people between ages 55 and 64 years, confers a substantial and long-lasting protection from colorectal cancer," the study's authors concluded.

Dr. Des Leddin, a gastroenterologist in Halifax who heads a national committee that has been waiting for the results before making new recommendations on the best way to screen for colon cancer, forecast quick action.

"I expect it'll be incorporated into our new guidelines within weeks," Leddin said, noting the widely anticipated findings have the ability to change practice.

If the British study experience were to hold in Canada, it could translate into almost 7,000 fewer cancers and 4,000 fewer deaths each year.

Leddin said Canada has a poor record in detecting colon cancer, although most provinces are now introducing a stool screening test for people over 50.

The findings could also make doctors rethink whether the less invasive, five-minute sigmoidoscopy of the lower bowel plus the sensitive fecal blood test could be better than a colonoscopy, said Dr. David Ransohoff of the departments of medicine and epidemiology, University of North Carolina at Chapel Hill, who was not part of the study but wrote an accompanying journal editorial.

With files from The Associated Press