NEWS

Last Decade Brought New Guidelines, Detection Methods for Colon Cancer Screening

Sarah L. Zielinski

When scientists met at the International Workshop on Colorectal Cancer Screening in 1994, widespread screening was still under discussion, regular colonoscopy was just being considered as an option for screening, and virtual colonoscopy was given one of its first public demonstrations.

Ten years later, there are now firm screening recommendations, and about half of eligible people get screened. But the options appear to be in transition and newer technologies, including virtual colonoscopy, have entered the pool.

Several organizations, including the U.S. Preventive Services Task Force, now recommend that all adults age 50 and older get screened for colon cancer by one of four methods: annual fecal occult blood test (FOBT), flexible sigmoidoscopy or barium enema every 5 years, or colonoscopy every 10 years. However, barium enema is "on the endangered species list," and sigmoidoscopy is close behind it, said Bernard Levin, M.D., vice president for cancer prevention at the University of Texas M. D. Anderson Cancer Center in Houston.

Results from some studies suggest that barium enema and sigmoidoscopy may not be as effective as FOBT and colonoscopy as screening tools, but they are still offered as options so that patients can choose which screening method is best for them based on their own and their physician's preference and what may be available in their area. "Any screening test is better than none," said Sidney Winawer, M.D., attending physician for gastroenterology and Paul Sherlock Chair at Memorial Sloan-Kettering Cancer Center in New York.




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The photos above show the same colon polyp as seen by virtual colonoscopy (left) and conventional colonoscopy. Virtual colonoscopy was introduced in 1994, and a National Institutes of Health audience got its first glimpse of the procedure on a videotape which, our News story from July 1994 noted, was accompanied by Wagner's "Ride of the Valkyries."

 

Each of the screening tests currently offered has its limitations, and researchers are searching for noninvasive tests that could be used to decide who needs the more invasive colonoscopy. Virtual colonoscopy, which uses a computed tomography (CT) scan and computer algorithms to produce two- or three-dimensional images of the colon, has been suggested as one of the possibilities.

At the University of Wisconsin in Madison, virtual colonoscopy has already taken its place as the first part in a two-part screening process. At the UW Hospital and Clinics, the first site where the procedure is covered by local insurance companies, patients receive a virtual colonoscopy in the morning and, for the 5% or less who need it, receive a conventional colonoscopy that same day, so patients have to go through the uncomfortable process of preparation for the exam only once.

Studies comparing conventional and virtual colonoscopy have had mixed results. Perry J. Pickhardt, M.D., associate professor of radiology at the University of Wisconsin Medical School, attributes the range of results to the variety of software programs used. "Too many researchers are trying to prove their way is right," he said, and those who are using old ways, particularly the two-dimensional software, have worse results than researchers who use the newest equipment and software.

The reliability and effectiveness of virtual colonoscopy to detect polyps depend on the software used and how well its users have been trained. Until the field comes to a consensus on the software and the best technology becomes available to everyone, the technique will not be ready for nationwide use, Pickhardt said.

Virtual colonoscopy is just one of several avenues researchers are pursuing in colon cancer screening. There have been efforts to improve the immunochemical assays now used with FOBT and to develop tests for gene or protein markers in stool or blood. Others have been working to refine conventional colonoscopy by developing self-propelled colonoscopes, engineering colonoscopes for magnification or spectroscopy, and introducing dye spraying for easier detection of polyps. And virtual colonoscopy could be made more acceptable by the development of a method that does not require the patient to undergo extensive bowel preparation.

Researchers will continue to search for noninvasive screening methods, convinced that early detection is the best path toward colon cancer prevention. "Mortality and incidence have declined at least over the last two decades, so something's working," said Levin.

NOTES

This is part of an occasional series that recalls some of the stories reported 10 years ago in the News section of the Journal.



             
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