Although colonoscopy is considered the gold standard for colon cancer screening and is used in millions of people every year, it hasn't been clear how its widespread use impacts the disease's overall death toll.
The new report, based on close to 2.5 million Canadians, shows that for every 1% increase in colonoscopy use, the risk of death from colon cancer dropped 3%.
"These procedures cost a lot, and we're doing an awful lot of them in the U.S. and in Canada," Dr. Linda Rabeneck, who led the research, told Reuters Health. "Now we know they work."
During a colonoscopy exam, the doctor inserts a slim, flexible tube into the rectum. A camera at the tip of the tube shows the inside of the colon and allows the doctor to identify small cell clumps that might one day turn into a cancer tumor. The tube, or scope, can also be used to biopsy or remove the abnormal cells.
Rabeneck, of the University of Toronto, said many countries have seen steep increases in the procedure since the 1990s, and it is recommended during routine colon cancer screenings of people older than 50 years.
For their study, Rabeneck and colleagues used healthcare databases from Ontario, Canada, to link colonoscopy rates and colon cancer deaths in the province over 14 years.
They followed more than 2.4 million people, who were between 50 and 90 years old at the outset of the study and did not have colon cancer. By 2006, about one in 100 had died from the disease, which mostly attacks older people.
Over the same period, as colonoscopy rates nearly quadrupled, the risk of dying from colon cancer tapered steadily, even after accounting for factors such as income and age.
The risk reduction presumably is achieved by removing abnormal cells before they become cancerous or, if they already are, before the cancer becomes aggressive, the researchers report in the American Journal of Gastroenterology.
The findings square with earlier research, although no one has tested the effect of colonoscopy on cancer death directly. Doing so would require a so-called randomized controlled trial -- the most powerful kind of study in the scientific toolbox -- in which participants are randomly assigned to screening or no screening.
Short of such a study, which is expensive, time-consuming, and possibly unethical, the new work "is as close as you can get," said Dr. John Allen, a colon cancer expert and a community practice counselor with the American Gastroenterological Association.
While the evidence isn't perfect, Allen, also of Minnesota Gastroenterology PA, said it was pretty clear by now that colonoscopy reduces colon cancer deaths.
"There are enough studies out there to cement the idea," he said.
By Frederik Joelving
Source: American Journal of Gastroenterology, online March 2, 2010.
Last Updated: 2010-04-02 8:00:04 -0400 (Reuters Health)
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