The study looked at more than 17,000 men and women ages 55-64 who said they were willing to take a colon cancer screening test.
That test: flexible sigmoidoscopy, an exam that requires a similar night-before bowel prep as a colonoscopy but which is much simpler and less risky to perform. While colonoscopies usually are performed with anesthesia and by a gastroenterologist, sigmoidoscopies require no sedation and can be performed by general practitioners or trained nurses.
The downside of sigmoidoscopy is that it can see only the left side of the colon. Can that really be enough to prevent colon cancer?
Yes, find Wendy S. Atkin, PhD, MPH, of Imperial College, London, and colleagues. Atkin's team was looking for a cost-effective way to screen the entire U.K. population for colon cancer. Early studies suggested that just a single sigmoidoscopy around age 60 could prevent colon cancer.
How? Sigmoidoscopy is just as good as colonoscopy at finding and removing precancerous colon polyps in the left side of the colon, where two out of three colon cancers arise. Atkin's research suggested that a look at the left colon can identify the minority of people who need a full colonoscopy -- and that it can also identify the majority of people who will never need another invasive colon screening test.
Now it seems that all this may be true. Eleven years later, people who got that single sigmoidoscopy had 33% fewer colon cancers and 43% fewer deaths from colon cancer.
"It's a one-off test ... and it probably will be done just once in a lifetime," Atkins said at a news briefing. "It works well to prevent cancer in the [left] bowel. We don't think it can prevent cancers higher up in the bowel, but we can detect them early using the existing [fecal occult blood] test."
Moreover, the study finds that colon cancer risk continues to decline in the years following flexible sigmoidoscopy.
"You'd think by now we'd see some sign of waning protection, but we see no waning at all," Atkin said. "I hypothesize it will last forever because I believe most of the polyps that are going to cause [left bowel] cancer are already there in your 50s. So all we have to do is look for them, find them, and remove them. And so far this hypothesis seems to be playing out."
Atkins and colleagues argue that in the government-funded U.K. health system, a single sigmoidoscopy at age 60 plus regular fecal occult blood test (a simple test for blood in the stool) will cut the colon cancer rate while lowering overall health care costs.
Implications for U.S. Colon Cancer Screening
What about the U.S., where the gold standard is colonoscopy every 10 years beginning at age 50?
Insight comes from John Monson, MD, chief of colorectal surgery at the University of Rochester, N.Y. Monson helped design the U.K. national training program that teaches nurses to perform sigmoidoscopies, and he also assisted in the design of the Atkin study (although he was not involved in the study itself).
"If you are fortunate enough to have insurance, assuming you are age 50 or so, then a colonoscopy is the right thing. But the reality is that large numbers of American patients do not have access to colonoscopy," Monson tells WebMD.
We shouldn't think of sigmoidoscopy as replacing colonoscopy, Monson says. Instead, we should think of it as a way to look for patients who truly need a colonoscopy.
"Flexible sigmoidoscopy is actually a very good use of health care resources to screen for people who should have a colonoscopy, which does have its downsides due to complications and costs," he says. "It is not simply flexible sigmoidoscopy, period. It is sigmoidoscopy followed by colonoscopy if you have certain findings. And it is pretty effective at preventing colon cancer."
The Atkin study appears in the April 28 online edition of The Lancet.