Screening colonoscopy showed its efficacy for preventing incident cases of colorectal cancer in prospectively collected data during follow-up of up to 24 years in about 170,000 average-risk Americans.
In general, the new findings support current public health recommendations for screening colonoscopy every 10 years in adults aged 50-75 years, said at the meeting.
The new results showed that screening colonoscopy can significantly cut the risk for new onset colorectal cancer by 51% that the benefit from a single colonoscopy screen extended beyond 7 years, and that colonoscopy worked better than screening sigmoidoscopy, said a gastroenterologist at the University of Aberdeen (Scotland).
The study used data from two large, prospective US observational studies: the Nurses’ Health Study, which began in 1976 and initially included 121,700 US women, and the Health Professional Follow-Up Study, which began in 1986 and included 51,529 men.
The database included more than 2 million person years follow-up from both studies, and during follow-up 2,198 participants developed new-onset colorectal cancer.
In the multivariate model, compared with no endoscopy, a negative colonoscopy result cut the rate of colorectal cancer by a statistically significant 51%, while negative sigmoidoscopy and polypectomy each cut the subsequent cancer rates by a statistically significant 37%.
A negative colonoscopy was the only procedure to cut the risk for incident proximal cancers significantly, reducing the rate by 26% compared with no endoscopy. For distal cancers, colonoscopy cut the rate by 71% compared with no screening, while sigmoidoscopy and polypectomy each cut the rate by 53%; all these risk reductions for distal cancers were significant.
In the analysis that assessed the durability of protection, screening colonoscopy cut the risk for new colorectal cancers by a statistically significant 34%, compared with no screening even when incident cancers were tallied more than 7 years following the index colonoscopy procedure. When cancers were divided by location, however, colonoscopy provided significant protection only for the first 3 years, with a risk reduction of 41% compared with no screening. Beyond that, colonoscopy did not produce a statistically significant reduction in incident cancers compared with no screening.
In contrast, for distal cancers that protective benefit of colonoscopy extended beyond 7 years: Screening colonoscopy provided a significant 42% cancer-rate reduction, compared with no screening, more than 7 years out.