Drs Brenner and Hoffmeister from Germany reviewed, summarized, and compared the evidence for effectiveness of screening sigmoidoscopy and screening colonoscopy in the prevention of colorectal cancer occurrence and deaths.
The team performed a systematic review and meta-analysis of randomized controlled trials and observational studies.
There were 2 investigators that independently extracted characteristics and results of identified studies, and performed standardized quality ratings.
The team identified randomized controlled trials and observational studies in English on the impact of screening sigmoidoscopy, and screening colonoscopy on colorectal cancer incidence and mortality in the general population at average risk.
|Summary estimates of reduction in distal colorectal cancer mortality were 61% in per protocol analysis|
|British Medical Journal|
For screening sigmoidoscopy, the team found 4 randomized controlled trials, and 10 observational studies that consistently found a major reduction in distal but not proximal colorectal cancer incidence and mortality.
The team observed that summary estimates of reduction in distal colorectal cancer incidence and mortality were 31% and 46% in intention to screen analysis, 42% and 61% in per protocol analysis of randomized controlled trials, and 64% and 66% in observational studies.
For screening colonoscopy, evidence was restricted to 6 observational studies, the results of which suggest tentatively an even stronger reduction in distal colorectal cancer incidence and mortality, along with a significant reduction in mortality from cancer of the proximal colon.
Indirect comparisons of results of observational studies on screening sigmoidoscopy, and colonoscopy suggest a 40% to 60% lower risk of incident colorectal cancer, and death from colorectal cancer after screening colonoscopy even though this incremental risk reduction was statistically significant for deaths from cancer of the proximal colon only.
Dr Brenner and colleague conclude, "Compelling and consistent evidence from randomized controlled trials and observational studies suggests that screening sigmoidoscopy and screening colonoscopy prevent most deaths from distal colorectal cancer."
"Observational studies suggest that colonoscopy compared with flexible sigmoidoscopy decreases mortality from cancer of the proximal colon."
"This added value should be examined in further research and weighed against the higher costs, discomfort, complication rates, capacities needed, and possible differences in compliance."