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.
Slideshow: Understanding Colorectal Cancer
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.