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TUESDAY, July 1, 2003 (HealthDayNews) -- Two new studies come to very different conclusions on the proper timetable for having sigmoidoscopy, the uncomfortable but effective test to screen for cancer of the colon and rectum.
American health officials currently recommend that healthy people have a sigmoidoscopy every five years. But a just-released study says there is, perhaps, a 1-in-100 chance that someone who tested negative will develop a cancer, or an intestinal growth that leads to cancer, within three years of the last exam.
Yet another study, using completely different methods, found that a single sigmoidoscopy reduced the risk of undetected cancer for as long as 15 years, suggesting the length of time between tests could be extended.
Sigmoidoscopy is the insertion of a flexible tube to inspect the lower portion of the colon, where 60 percent of all colorectal cancers occur. The tube allows doctors to look for polyps -- growths that can become cancerous. Most people who have a sigmoidoscopy must take an enema, and there is a slight risk that the intestine may be damaged.
The first study, done by Dr. Robert E. Schoen and colleagues at the University of Pittsburgh Cancer Institute, included 11,583 people who had an initial sigmoidoscopy and 9,317 who had a second examination three years later.
Of the second group, 1,292 of the people were found to have some sort of intestinal growth in the second examination, says a report in the July 2 Journal of the American Medical Association. Follow-up exams of 951 of the people revealed that 72 had a precancerous polyp, and six had a cancer.
"Although the overall percentage with detected abnormalities is modest, these data raise concern about the impact of a prolonged screening interval after a negative examination," the researchers write in the journal.
The other study, led by Polly A. Newcomb, director of prevention at the Fred Hutchinson Cancer Research Institute in Seattle, collected information on screening history and colorectal risk factors from 1,668 cancer patients and 1,294 healthy people.
There was a four-fold reduction in the incidence of cancer in the distal region of the colon -- the part inspected during sigmoidoscopy -- for people who recalled having at least one sigmoidoscopy, compared to those who said they never had one. The reduction in cancer lasted for at least 15 years, says the report in a recent issue of the Journal of the National Cancer Institute.
The University of Pittsburgh's Schoen says the second study's conclusion is open to question because it relied on potentially unreliable self-reporting to determine who had had sigmoidoscopies.
But Newcomb says "we have found that people can accurately report if they have had a sigmoidoscopy."
Newcomb says her study argues for lengthening the recommended period between sigmoidoscopies. It takes a long time for most polyps to become cancerous, she says.
"The five-year period recommended by organizations such as the American Cancer Society doesn't appear to be data-based, unlike other recommendations," she contends.
Schoen, who is an associate professor of medicine and epidemiology at the Pittsburgh center, says he is not proposing a change in the five-year recommendation "at this time."
"We need more data," Schoen says, adding he'd like to see what the cancer rate was five years after the first screening. "Maybe it's not that different."
Because of issues such as "cost, complications, capacity [to do the testing], I don't think the results of [his] paper should be interpreted as saying that everyone has to come back in three years," Schoen says.
But "it does look like the more screening, the less the chance of missing something," he says.
More information
To learn more about colorectal cancer and sigmoidoscopy, visit the National Library of Medicine.
