PITTSBURGH, July 1 -- According to findings published in the July 2 issue of the Journal of the American Medical Association (JAMA), repeating flexible sigmoidoscopy three years after a negative exam can detect advanced adenomas (pre-cancerous polyps or growths in the lining of the large intestine) and distal colon cancer, raising concern about the impact of delaying repeat screening for prolonged intervals.
"Our study found a three- to four-fold increase in detection from the initial exam compared to the next exam three years later. The findings at three years, although modest, indicate that more frequent screening for colon cancer, by detecting pre-cancerous growths, could have an impact on mortality from this disease," said Robert Schoen, MD, MPH, lead author of the study and associate professor of medicine and epidemiology, University of Pittsburgh School of Medicine. "Our findings raise concern that a longer interval between exams, such as the currently recommended 10-year interval for repeat colonoscopy after a negative exam, may result in morbidity and mortality from colorectal cancer. This is especially suggested by the fact that more than 80 percent of the advanced lesions found on the repeat exam three years later were found in a region of the colon that, as far as can be determined, was well examined the first time around," added Schoen, who also is director of colorectal and gastrointestinal cancer prevention and control research at the University of Pittsburgh Cancer Institute.
During flexible sigmoidoscopy (FSG), a doctor uses a lighted scope to examine the inside of the large intestine from the rectum through the descending colon, where most colon polyps develop.
The study included individuals enrolled in the Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) Screening Trial, a randomized, community-based study evaluating the effectiveness of cancer screening tests on site-specific mortality that has enrolled nearly 155,000 people at 10 centers in the United States. Subjects in the study were eligible for repeat FSG three years after an initial negative result. The mean age of those who returned for repeat screening was 65.7 years. Of the 9,317 individuals who returned for repeat FSG, 13.9 percent (1,292) had a polyp or mass, 3.1 percent (292) were found to have a non-advanced adenoma and 0.8 percent had an advanced adenoma or cancer in the distal colon.
"While the overall percentage of detected abnormalities was modest, these data question the notion that individuals with initial negative results can wait for prolonged periods of time to be re-screened," says Schoen.
Colorectal cancer is a worldwide public health problem. In the United States, colorectal cancer accounts for 11 percent of all cancers, with 147,330 new cases and 56,000 deaths expected in 2002. For patients with advanced disease, five-year survival rates are 10 to 20 percent. However, when colorectal cancer is diagnosed at an early, localized stage, the five-year survival rate is 90 percent.
Co-authors of the study include Joel L. Weissfeld, MD, MPH., University of Pittsburgh; Paul F. Pinsky, PhD., Philip Prorok, PhD., and John K. Gohagan, PhD., National Cancer Institute; Robert S. Bresalier, MD, MD Anderson Cancer Center; and Timothy Church, PhD, University of Minnesota.
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