TUESDAY, May 20 (HealthDay News) -- The people who most need to have repeat colonoscopies to detect precancerous growths are less likely to get the potentially lifesaving procedures, new research shows.

"We are doing more colonoscopies among the low-risk groups and not enough among the high-risk," study author Dr. Adeyinka Laiyemo, a cancer prevention research fellow at the National Cancer Institute, said during a press conference Monday at Digestive Disease Week 2008 in San Diego.

In a colonoscopy, a thin, lighted flexible tube with a tiny video camera is eased into the colon and a tiny camera transmits pictures to a TV screen. Small air puffs put into the colon keep it open and allow the doctor to see it clearly.

Laiyemo reported on the follow-up to the Polyp Prevention Trial, in which his team continued to follow those participants after the trial ended. The original trial was a four-year study in which some patients were randomly assigned to eat a low-fat, high-fiber diet with plenty of fruits and vegetables to see if it would prevent the recurrence of polyps, growths that can develop into colon cancers.

Of the 2,079 enrolled in the trial, 92 percent finished it, having an average of 3.1 colonoscopies, procedures that can detect colon cancer in early and curable stages. Of those, 1,297 patients agreed to be followed up by providing their subsequent colonoscopy reports.

During the six or more years of follow-up, 774 had repeat procedures. But while 30 percent of the patients termed low-risk (because they had a low risk of polyps at the end of the trial), just 41 percent of those classified as high risk of recurrence had repeat colonoscopies.

A second study, also presented at the conference, continues to support colonoscopy as the first line of detection for polyps. "The bigger the polyp, the greater the chance [the colon] has cancer already or it is going to turn into it," said Dr. Douglas Rex, a professor of medicine at Indiana University School of Medicine and director of endoscopy at Indiana University Hospital, in Indianapolis.

In his study, Rex wanted to evaluate the impact of a new recommendation from the American College of Radiology, recommending that polyps 5 millimeters or smaller not be reported on CT colonography (CTC), also called virtual colonoscopy, a procedure in which a detailed picture of the colon is created by an X-ray machine linked to a computer. The recommendation also suggests those with one or two polyps that are 6 millimeters to 9 millimeters be offered CTC surveillance in three years instead of polyp removal.

Rex's team looked at more than 10,000 polyps over a five-year period after they had colonoscopies. They wanted to figure out how many patients would have been identified as higher risk if they had CTC as their first test instead of colonoscopy, doing so by evaluating the numbers and sizes of polyps.

If CTC had been used as the first test, and if the CTC had been 100 percent accurate at finding polyps over 5 millimeters, then 29 percent of all the patients and 30 percent of those over age 50 with high-risk polyps would have been classified as normal, he said.

In another presentation, the shorter the interval between completing the bowel cleaning preparation required before colonoscopy and the start of the procedure, the better.

"Colonoscopy started within 14 hours of the last preparation had better quality," said study author Dr. Ali Siddiqui, an assistant professor of internal medicine at the University of Texas Southwestern Medical Center at Dallas.

His team gathered information over a three-month period on 378 outpatients who had colonoscopies done at a VA Medical Center.

The American Cancer Society expects more than 108,000 cases of colon cancer diagnoses this year, plus another 40,000 cases of rectal cancer. Almost 50,000 people in the United States will die of colorectal cancer this year, the society estimates.

More information

For more on colonoscopies, go to the National Institute of Diabetes and Digestive and Kidney Diseases.

SOURCES: May 19, 2008, teleconference with Adeyinka O. Laiyemo, M.D., Cancer Prevention Fellow, National Cancer Institute, Bethesda, Md.; Douglas Rex, M.D., professor, medicine, Indiana University School of Medicine, and director, endoscopy, Indiana University Hospital, Indianapolis; Ali Siddiqui, M.D., assistant professor, internal medicine, University of Texas Southwestern Medical Center at Dallas; May 19, 2008, presentations, Digestive Diseases Week 2008, San Diego

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