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Flexible sigmoidoscopy reduced colorectal cancer incidence by one-third
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When offered only once to patients aged 55 to 64 years, flexible sigmoidoscopy use reduced the incidence of colorectal cancers by about one-third, according to the long-term results of a large U.K. study published in The Lancet.
In addition, the study, conducted by Wendy S. Atkin, PhD, and colleagues from the U.K. Flexible Sigmoidoscopy Trial Investigators, found that flexible sigmoidoscopy reduced the incidence of distal colorectal cancer by half.
“The good news is that this size of benefit is large for any cancer screening test, certainly compared with mammography for breast cancer or assay of PSA for prostate cancer,” David F. Ransohoff, MD, from the department of medicine and epidemiology, University of North Carolina, Chapel Hill, wrote in an accompanying editorial. “On the other hand, a 50% reduction of colorectal cancer incidence (for lesions reached by the scope) is lower than figures popularly quoted for colonoscopy but on the basis of non-randomized data.”
The study was a randomized controlled trial that took place at 14 centers in the United Kingdom. During a period of 11 years, 170,432 men and women were randomly assigned flexible sigmoidoscopy (n=113,195) or usual care (n=57,237). A single flexible sigmoidoscopy was conducted using the Flexi-Scope, which is only currently available in the United Kingdom through a referral from a general practitioner or specialist for patients with symptoms. Seventy-one percent of patients attended their sigmoidoscopy.
Of the patients randomized, 112,939 of the flexible sigmoidoscopy group were included in the final analysis; 57,099 from the usual care group were included.
Colorectal cancer, mortality
With a median follow-up of 11.2 years, 2,617 colorectal cancers were diagnosed in 2,524 patients: 1,818 were diagnosed in the usual care group vs. 706 in the intervention group. In the intention-to-treat analysis, patients who underwent flexible sigmoidoscopy had a 23% reduced risk for colorectal cancer (95% CI, 0.60-0.76) and a 13% reduced risk for mortality (95% CI, 0.59-0.82). In the per-protocol analysis, which the researchers adjusted for the self-selection bias in the intervention group, people who attended the flexible sigmoidoscopy had a 33% reduced risk for colorectal cancer (95% CI, 0.60-0.67) and a 43% reduced risk for mortality (95% CI, 0.45-0.72).
There were 20,543 deaths in the cohort; 727 were due to colorectal cancer (538 in the usually care group vs. 189 in the intervention group).
Distal, proximal cancers
Of the total diagnosed colorectal cancers, 1,192 people in the control group and 386 in the intervention group were diagnosed with distal cancers; 628 in the control group and 311 in the intervention group were diagnosed with proximal cancers. In the intention-to-treat analysis, screening reduced distal cancers by 36%, and proximal cancers by 2%. However, in the per-protocol group, screening reduced distal cancers by 50% and proximal cancers by 3%.
“Perhaps even greater reduction for screening sigmoidoscopy will be observed after more follow-up in the United Kingdom and Norwegian randomized trials, because long follow-up is needed to account for the ‘prevalent (screen detected) colorectal cancers [that] dilute any incidence reducing effect of polypectomy,’ as well as to detect mortality reduction,” Ransohoff wrote. “… More frequent endoscopy might lead to still greater reductions in colorectal cancer, as may be assessed in the United States randomized trial of screening sigmoidoscopy repeated at five years. In 2010, the U.K. randomized study must be regarded as the most reliable evidence about the size of the reduction in colorectal cancer for 10 years after endoscopic examination of the left colon.”
For more information:
- Atkin WS. Lancet. 2010:doi10.1016/S0140-6736(10)60551-x.
- Ransohoff DF. Lancet. 2010:doi:10.1016/S0140-6736(10)60626-5.