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More frequent screening would improve detection of colon cancer

Scott Gottlieb New York

Examining the colon more frequently than is currently recommended may improve detection and prevention of cancer, according to the preliminary results of a large study.

The prostate, lung, colorectal, and ovarian cancer screening trial is a randomised controlled, community based study that is evaluating the effect of cancer screening on mortality from site specific cancers. Sponsored by the US National Cancer Institute, the trial is being conducted in 10 screening centres in the United States.

Between 1993 and 2001 the trial enrolled more than 154000 people aged 55 to 74 years. They will be followed until 2013. The patients were randomly assigned to receive different tests, including flexible sigmoidoscopy.

The preliminary report gives the findings on patients who underwent flexible sigmoidoscopy at baseline and at three years (following the trial’s protocol) and were referred to their personal doctors for further evaluation of any abnormalities detected by the screening (JAMA 2003;290:41-8). A polypoid lesion or mass found by the examiner was considered a positive result of screening.

About 11500 patients who had flexible sigmoidoscopy and were found to be free of polyps and cancer were told to come back in three years’ time for another examination. Eighty per cent of the patients, or 9317, returned. Of these, 1292 (14%) had abnormal growths, and 292 were found to have cancer. The total incidence of adenoma or cancer in the distal colon three years after a negative result of flexible sigmoidoscopy was 3.1%.

A quarter of the patients with adenomas had advanced adenomas, and six distal colon cancers were detected, giving an incidence of advanced distal lesions of 0.8%. Although it cannot be determined whether these lesions were missed at the initial screening or whether they developed over the three year observation period, 81% of patients with advanced distal adenomas had lesions in a portion of the colon that had been adequately examined at the initial sigmoidoscopy.

The finding is important, because even patients who were carefully examined at the first screening had polyps or even cancer within three years. Currently, most patients are told to have flexible sigmoidoscopy once at the age of 50 and then every five years if nothing is found (Gastroenterology 2003;124:544-60). For colonoscopy the recommendation is once every 10 years if the first examination is negative (Gastroenterology 1996;111:1178-81).

"The findings at three years, although modest, indicate that more frequent screening for colon cancer, by detecting precancerous growths, could have an impact on mortality from this disease," said Dr Robert Schoen, lead author of the study and an associate professor of medicine and epidemiology at the University of Pittsburgh School of Medicine.

Dr Schoen said patients should not necessarily think that a negative result is a permanent clean bill of health. "If you had a colonoscopy last year, I think at five years you might want to check in with your physician and see if there’s anything new that’s been learned [about colon cancer screening]," he said.