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A simple, cheaper exam of just the lower part of the large intestine can cut the risk of developing colon cancer or dying of the disease, a new study has found.
Many doctors recommend a more complete test — colonoscopy — but many people refuse that costly, unpleasant exam.
The new study shows that the simpler test, flexible sigmoidoscopy, can be a good option, though it misses about a quarter of the cancers that a colonoscopy would catch.
Experts said that even a partial bowel exam is better than none. As one put it, "the best test is the one that gets done."
The study was published online Monday by the New England Journal of Medicine.
Colorectal cancer is the second-leading cause of cancer deaths for Canadian men and the third-leading cause of cancer deaths for Canadian women, according to the Canadian Cancer Society. About 23,300 new cases and 9,200 deaths from the disease are expected this year alone.
People ages 50 to 75 who are at average risk of colon cancer are urged to get screened, but only about 50 per cent do. The trend is improving, though: nine years ago, screening rates were below 30 per cent in Canada.
Advice varies on the best way to get screened. The recommendation of the government of Ontario, where colorectal cancer rates are among the highest in the world, is that everyone over age 50 have a stool sample called a fecal occult blood test every two years. People with a family history of the disease should have a colonoscopy every five to seven years.
The problem is that a colonoscopy requires a day of preparation and fasting, including drinking strong solutions to clean out the bowel. During the procedure, patients are sedated before a thin tube with a tiny camera is guided through the large intestine. Growths can be removed and checked for cancer.
Sigmoidoscopy also uses a thin scope and tiny camera, can be done in an ordinary doctor's office, requires much less bowel preparation and costs far less.
One drawback: It sees only the lower third of the colon, "but that is an area where probably half of polyps and cancers develop," said Dr. Durado Brooks, the American Cancer Society's colon cancer expert.
The new study, led by Dr. Robert Schoen of the University of Pittsburgh Medical Center, tested how well flexible sigmoidoscopy works.
From 1993 to 2001, about 155,000 people aged 55 to 75 were assigned to one of two groups. The first set got a sigmoidoscopy at the start of the study and again three to five years later, while the second cohort got screening by whatever means they or their doctors wanted. Any patients with suspicious findings were sent for a colonoscopy.
After about 12 years of follow-up, there were 21 per cent fewer cases of colon cancer and 26 per cent fewer deaths from the disease in the group assigned to get flexible sigmoidoscopy.
Of the cancers in that group, 243 were considered to have been caught by sigmoidoscopy (many others were found because of symptoms or other tests). Researchers estimate that 97 more would have been detected if colonoscopy had been the main screening method instead of the simpler scope exam, said study co-leader Dr. Christine Berg, chief of early detection research at the U.S. National Cancer Institute, which sponsored the research.
"My opinion is that there's no doubt that colonoscopy would be better in detecting more total cancers," she said. "A sigmoidoscopy could be used in situations where people are afraid of having the bowel prep," or when sedation is a risk, she said.
The results reinforce that colonoscopy is a better screening method, but suggest that conscientious screening with sigmoidoscopy is still better than the de facto practices of patients, half of whom don't go for any screening.
If those screening rates improved, of course, sigmoidoscopy would be less relatively useful.
Previous research in Britain has also found that screening with flexible sigmoidoscopy is an effective way to reduce cancer mortality, but that was in comparison with a control group in the study that underwent no screening at all.
With files from CBC News
