The study involved almost 155,000 men and women aged 55 to 74. About half underwent flexible sigmoidoscopy screening upon entering the study and again three years to five years later. In this procedure, a long, flexible tubular instrument about 1/2 inch in diameter is used to view the lining of the rectum and the lower third of the colon.
The rest received standard colon cancer screening if they asked for it, or if their doctor recommended it. There are several tests that are considered options for colon cancer screening. Colonoscopy, considered the gold standard, is one of these options, and for screening is typically performed every 10 years beginning at age 50. A colonoscopy procedure allows for visualization of the entire colon.
Flexible sigmoidoscopy has a number of benefits over the more invasive colonoscopy. It requires less bowel prep, less sedation, has fewer side effects, and is much simpler to perform. There's also a lower risk of bowel perforation, in which the screening instrument pokes a hole in the intestine; while uncommon with colonoscopy, it's enough to scare some people off. And, flexible sigmoidoscopy is cheaper.
The disadvantage of sigmoidoscopy is that it only allows the doctor to view and remove precancerous colon polyps from the left side of the colon, where two out of three colon cancers develop.
Still, that look at the left side was enough to identify most people who needed full colonoscopies, says researcher Robert E. Schoen, MD, MPH, professor of medicine and epidemiology at the University of Pittsburgh.
Colon Cancer Cases, Deaths Cut
After nearly 12 years, people in the sigmoidoscopy group were 21% less likely to have colon cancer and 26% less likely to die from colon cancer than those in the standard care group.
That means that over the course of 10 years, there would be three fewer new cases and one less death from colorectal cancer if 10,000 people had two regular sigmoidoscopy screenings vs. standard care, Schoen says.
But a closer look at the data shows that the benefit was attributable to the 22% of people who underwent follow-up colonoscopies as a result of suspicious findings on sigmoidoscopy, he tells WebMD.
Cases and deaths from colon cancer in the left colon were slashed by 29% and 50%, respectively. Cases in the right colon were reduced by 14%, with no substantial dent in the death rate.
The results appear online in The New England Journal of Medicine and were presented at Digestive Disease Week in San Diego.
The Best Screening Test: The One You Get
So are you better off getting a colonoscopy? Or a sigmoidoscopy?
That's one question, Schoen and other experts agree, where the answer doesn't matter -- as long as you get something.
"What this study clearly says is that if you don't want a colonoscopy, have a sigmoidoscopy or a fecal occult blood test. Just have something. Colorectal cancer screening is a homerun in its ability to reduce new cancers and cancer deaths," Schoen says.
Barnett Kramer, MD, director of the National Cancer Institute's division of cancer prevention, notes that this is the second major trial to show that sigmoidoscopy is effective in reducing the risk of colorectal cancer.
"Sigmoidoscopy is less invasive than colonoscopy and carries a lower risk of the colon being perforated, which may make it more acceptable as a screening test to some patients. There are several effective screening tests for colon cancer, and the most effective screening test is the one that people choose to take," he said in a statement.
David Bernstein, MD, a gastroenterologist at North Shore University Hospital in Manhasset, N.Y., notes that there haven't been any clinical trials directly comparing sigmoidoscopy to colonoscopy.
"This study clearly shows that sigmoidoscopy reduces colorectal cancer cases and deaths for the segment of colon it is supposed to evaluate" and therefore is a good use of health care resources to screen for people who should have a colonoscopy, he says.
"But the take-home message is that we have not just one, but several excellent methods to prevent colon cancer," Bernstein tells WebMD.
John M. Inadomi, MD, a gastroenterologist at the University of Washington in Seattle, wrote an editorial accompanying the study. "Patients preferences for screening tests should be identified and respected -- in this case, the best test is the one that gets done," he writes.