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Flexible sigmoidoscopy looks at about a third of the colon, as compared to the whole colon as is seen in colonoscopy. But unlike colonoscopy, sigmoidoscopy does not typically require sedation.
However, new research finds that while sigmoidoscopy is associated with fewer colon cancer cases and deaths for men who undergo the screen, that benefit was not observed for women.
"For women, we could not detect an effect of sigmoidoscopy screening on [colon cancer] incidence or mortality," wrote a team led by Dr. Oyvind Holme, of the University of Oslo in Norway.
As Holme's team explained, prior research has suggested that sigmoidoscopy reduces overall colon cancer incidence by 18 percent to 26 percent, and related deaths by 22 percent to 31 percent over 10 to 17 years.
But it's not been clear if both genders benefit equally.
In this study, nearly 99,000 Norwegians aged 50 to 64 were randomly selected to undergo sigmoidoscopy screening for colon cancer, or to have no type of screening.
After 17 years, men in the sigmoidoscopy group had a 34 percent lower risk of colon cancer and a 37 percent lower risk of death from the disease than men in the non-screening group.
However, women in the sigmoidoscopy group saw little reduction in their colon cancer risk or death rates, compared to women who weren't screened, the findings showed.
The study was published online April 23 in Annals of Internal Medicine.
Why the difference by gender? In an accompanying journal editorial, Dr. Kirsten Bibbins-Domingo of the University of California, San Francisco, pointed out that colon cancer tends to progress differently in men and women.
She noted that the peak incidence of colon cancer occurs at an earlier age in men than in women. That means that with a one-time sigmoidoscopy screening, the age at which women were screened may have been too early to spot those who would go on to develop colon cancer, Bibbins-Domingo theorized.
More research is needed to identify the best colon screening strategy for women, she said.
Dr. Arun Swaminath directs the inflammatory bowel disease program at Lenox Hill Hospital in New York City. He said that, in his own practice, he prefers the use of colonoscopy to sigmoidoscopy because the former examines more of the colon.
"That being said, [expert guidelines] approve sigmoidoscopy to be one of the screening options for colon cancer in the United States," Swaminath said.
But the Norwegian study found sigmoidoscopy "didn't seem to benefit women as it did men," he said. "The implication, if it's confirmed in a U.S. population, is that women should not be offered sigmoidoscopy [with or without a stool test] as a screening test as it doesn't seem to offer benefit."
On the positive side -- at least for men - "the [protective] benefit of a sigmoidoscopy seems to last well beyond five years, the typical interval before repeat studies are currently recommended," Swaminath noted.
That could mean that testing might need to be done less often, potentially saving health care dollars, he suggested.
-- Robert Preidt
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SOURCES: Arun Swaminath, M.D., director, inflammatory bowel disease program, Lenox Hill Hospital, New York City; Annals of Internal Medicine, news release, April 23, 2018