Colonoscopy Better Than Alternative at Spotting Cancer in Seniors: Study

TUESDAY May 10, 2011 -- Colonoscopy is significantly better than the less expensive screening procedure called sigmoidoscopy at detecting colon cancer in older patients, a new study says.

"We imagined there would be some difference, but there's a four-fold difference" between the two screening tests when it comes to detecting cancer, said study lead author Dr. Yize Richard Wang, a fellow at the Mayo Clinic in Jacksonville, Fla.

"Colonoscopy still remains the gold standard," added Wang, a health economist.

In the United States, colon cancer kills more than 51,000 people a year, according to the National Cancer Institute. Screening helps identify cancer before symptoms appear, when it may be easier to treat.

Colonoscopy, the most common screening test for colon cancer, involves threading a scope with a tiny camera through the length of the colon. But patients can also choose flexible sigmoidoscopy, which uses a shorter scope, costs less and may be more comfortable. However, sigmoidoscopy examines only half or less of the colon, Wang said.

Years ago sigmoidoscopy was the main screening test for colon cancer, but it has become less common over time. However, "from a patient perspective, the preparation and discomfort associated with a sigmoidoscopy is often considered less burdensome," said Dr. Thomas Semrad, assistant professor of internal medicine at the University of California, Davis Medical Center, who's familiar with the study findings.

Using a national database, the study authors examined the records of 52,236 patients 67 or older who underwent colonoscopy or sigmoidoscopy between 1998 and 2005 and were diagnosed with colon cancer within three years of the procedure. According to the study abstract, 57,412 colonoscopies were performed, as were 3,523 sigmoidoscopies.

The percentage of new or missed left-sided colon cancers was 12 percent among the sigmoidoscopy patients but only 4 percent for the colonoscopy patients.

It's not clear why colonoscopy was better at detecting cancers, Wang said, but it may be because the sigmoidoscopy misses part of the colon.

"If you suspect the patient has colon cancer, colonoscopy is still a better test than flexible sigmoidoscopy," he said.

Differences in bowel preparation and lack of sedation might also help explain the variation, the study authors said, noting further research is necessary.

The study was to be presented Tuesday at the Digestive Diseases Week conference in Chicago. The research is considered preliminary because it has not been subject to the scrutiny required for publication in a peer-reviewed journal.

Although the study did not include people younger than 67, "the results might be similar," Wang said.

Semrad said sigmoidoscopy may be appropriate in some cases. Compared to a colonoscopy, "an individual sigmoidoscopy will cost less, be easier to perform, and in the right hands can be an appropriate screening test," he said.

"Ultimately, the right test will be different for different patients and different health systems," Semrad added.

The U.S. Preventive Services Task Force recommends colonoscopy screening every 10 years for people 50 to 75 years old who are considered at average risk of getting colon cancer.

It's important that people undergo screening, Semrad said. "We know that we could save thousands of lives each year if everyone was screened according to the guidelines," he added.

But some people have a fear of the procedure, he noted. "Because the preparation is easier and the discomfort is often less, [sigmoidoscopy] can be especially important testing for patients unwilling to undergo colonoscopy," he noted.

More information

For more about colon cancer, visit the U.S. National Library of Medicine.

Posted: May 2011


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