Because the UK guidelines recommend people at high risk of cancer come back one year after their initial colonoscopy, more worrisome polyps could be caught early than in the U.S., where the wait time between exams is typically three years, researchers said.

The new analysis deals with surveillance after patients have colon polyps caught on a colonoscopy, not routine cancer screening in those without symptoms.

"The main difference is the one-year colonoscopy, and how the U.S. doesn't have that for their high-risk group, whereas the UK does," said Maria Elena Martinez, from the University of California, San Diego, who led the new study.

"The findings highlight the importance of continuing to visit the data, and keep looking at the evidence that exists" when developing new surveillance guidelines, she told Reuters Health.

The UK and U.S. guidelines also differ in how they classify patients and their risk of cancer, based on the size and number of polyps removed during their colonoscopy - and in the U.S., based on characteristics of those polyps.

One or two small polyps qualify a person as low risk under both guidelines, with a recommended follow up at five to 10 years in the U.S. and five years or more in the UK.

From there, the U.S. guidelines - co-sponsored by the American Cancer Society (ACS) - go on to categorize some patients as higher-risk, with a recommended follow up of three years, and a small minority as highest-risk, when a second colonoscopy is called for within less than three years.

The UK classifies other patients as either intermediate-risk, with recommended follow up at three years, or high-risk, with another colonoscopy recommended after just one year.

According to the ACS, just over one in 20 people in the U.S. will be diagnosed with colorectal cancer during their lifetime.

To compare how patients might fare under each set of guidelines, Martinez and her colleagues used data from four U.S. studies, including 3,226 patients who had a first exam to find and remove colon polyps and a second surveillance colonoscopy within a year and a half.

At one year, about 4 percent of U.S. low-risk patients and 11 percent of higher-risk patients were diagnosed with pre-cancerous or advanced polyps. According to UK criteria, 4 percent of low-risk, 10 percent of intermediate-risk and 19 percent of high-risk people were diagnosed.

Martinez's team calculated that about one in five people with advanced polyps at one year would have been detected earlier under UK screening guidelines. That worked out to 53 of all 3,226 patients, or 1.6 percent, that would benefit from the UK criteria.

At the same time, there would be a slight increase in the average number of colonoscopies per patient from 1.42 over five years to 1.45, the researchers wrote in the Annals of Internal Medicine.

Getting too many colonoscopies is a concern because they can lead to complications such as bleeding and perforations or to false positives and more unnecessary tests and procedures.

PRACTICE "ALL OVER THE MAP"

Martinez said her team isn't recommending a total switch to UK guidelines, just continued review of U.S. ones.

Moving toward UK guidelines "would be a slightly more aggressive shift," said Dr. Michael LeFevre, co-vice chair of the U.S. Preventive Services Task Force and a professor the University of Missouri School of Medicine in Columbia.

"More patients would be coming back, and we don't know for sure the impact of that, other than we might find some (pre-cancerous and advanced polyps) in a year."

But, he pointed out, researchers don't know whether that would have an impact on what people really care about: cancer cases and cancer deaths.

LeFevre, who wasn't involved in the new study, told Reuters Health doctors in the U.S. aren't necessarily following any guidelines when they decide when to bring patients back for follow up colonoscopies.

"From a primary care provider perspective, I think the recommendations that come from gastroenterologists are all over the map," he said.

"Neither of these approaches is necessarily the approach that is being utilized."

For people who've had polyps removed during a colonoscopy, he said, it might be worth it to discuss follow up care with their doctors - including what type of treatment various guidelines recommend.

SOURCE: bit.ly/UNeD4z Annals of Internal Medicine, online December 17, 2012.

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