CHAPEL HILL – Among people who have had an initial colonoscopy that found no polyps, a possible sign of cancer, the risk of developing colorectal cancer within five years is extremely low, a new study has found.
"For that reason, once someone has had a negative initial colonoscopy, there is no need for that person to have another colonoscopy sooner than five years after that screening," said David F. Ransohoff, M.D., a professor in the University of North Carolina at Chapel Hill School of Medicine and senior author of the study, published in the Sept. 18, 2008, issue of The New England Journal of Medicine.
The lead author is Thomas F. Imperiale, M.D., of Indiana University, with whom Ransohoff has collaborated on several colonoscopy studies.
Ransohoff, also a member of UNC's Lineberger Comprehensive Cancer Center, said the latest study confirms what most gastroenterologists already believed, but it is the first large, formal study to confirm this conclusion. The report is also an important step to determine the appropriate interval for rescreening, he said.
"The current recommendations call for rescreening 10 years after an initial negative colonoscopy," he said. "Now, based on the results of this study, we know that there's no need to rescreen sooner than five years later. But we still don't know exactly how long the appropriate screening interval should be, so that's a question that future studies should address."
In the study, 2,436 people were identified who showed no signs or precursors of cancer after an initial colonoscopy. Of these, 1,256 or 56 percent were rescreened five years later. None who were rescreened were found to have cancer. One or more adenomas (polyps) were found in 201 people (16 percent) and of these 16 people (1.3 percent) had advanced adenomas (precancerous polyps). Men were more likely than women to have any type of adenoma and to have an advanced adenoma.
"These findings suggest that among persons who are at average risk for colorectal cancer, rescreening colonoscopy need not be performed sooner than 5 years after an initial colonoscopic examination with normal findings," the study concluded.