Study questions interval for screening sigmoidoscopy

A new study suggests that screening sigmoidoscopy is associated with a long-term reduction in the incidence of colorectal cancers for up to 16 years--a finding that suggests that the currently recommended screening interval of 5 years may be too aggressive. The study appears in the April 16 issue of the Journal of the National Cancer Institute.

Unlike colonoscopy, which examines the entire large bowel (colon and rectum) for precancerous polyps, sigmoidoscopy examines only the lower part of the organ. Nevertheless, this region accounts for more than 60% of all colorectal cancers. Sigmoidoscopy is associated with a reduction in the incidence of and mortality from colorectal cancer, and current guidelines recommend screening with sigmoidoscopy every 5 years. However, previous research has suggested that the screening interval could be lengthened, given that polyps may take up to 15 years to progress to cancer.

To examine the impact of sigmoidoscopy screening on colorectal cancer incidence, Polly A. Newcomb, Ph.D., of the Fred Hutchinson Cancer Research Center in Seattle, and her colleagues collected information on screening history and colorectal cancer risk factors from a population-based sample of 1,668 patients with either distal or proximal colorectal cancer and 1,294 healthy individuals.

Compared with individuals who had never had a screening sigmoidoscopy, individuals who had ever had a screening sigmoidoscopy had a four-fold reduction in the incidence of distal colorectal cancers. These reductions appeared to be sustained for more than 15 years, a finding that supports a longer screening interval than currently recommended, the authors say.

In an accompanying editorial, Jack S. Mandel, Ph.D., of Emory University, Altlanta, cautions that it may be premature to recommend lengthening the screening interval. "A more precise estimate of the benefit from sigmoidoscopy screening will have to await the results from the ongoing [randomized controlled trials]," he says. "At that time, we will be in a better position to more accurately evaluate the risks, benefits, and cost-effectiveness of screening. Those results will provide a better basis on which to develop screening policy."

Contact: Kristen Woodward, Fred Hutchinson Cancer Research Center, 206-667-5095; fax: 206-667-7005, kwoodwar@fhcrc.org.

Editorial: Tia Webster, Emory University, 404-727-5692; fax: 404-727-4392, twebste@emory.edu.

Newcomb PA, Storer BE, Morimoto LM, Templeton A, Potter JD. Long-term efficacy of sigmoidoscopy in the reduction of colorectal cancer incidence. J Natl Cancer Inst 2003;95:622–5.

Editorial: Mandel JS. Sigmoidoscopy screening probably works, but how well is still unknown. J Natl Cancer Inst 2003;95:571–3.

Note: The Journal of the National Cancer Institute is published by Oxford University Press and is not affiliated with the National Cancer Institute. Attribution to the Journal of the National Cancer Institute is requested in all news coverage.

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