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Time to Benefit for Colorectal Cancer Screening: Survival Meta-Analysis of Flexible Sigmoidoscopy Trials


Time to Benefit for Colorectal Cancer Screening: Survival Meta-Analysis of Flexible Sigmoidoscopy Trials

Victoria Tang et al. BMJ.

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Objective: To determine the time to benefit of using flexible sigmoidoscopy for colorectal cancer screening.

Design: Survival meta-analysis.

Data sources: A Cochrane Collaboration systematic review published in 2013, Medline, and Cochrane Library databases.

Eligibility criteria: Randomized controlled trials comparing screening flexible sigmoidoscopy with no screening. Trials with fewer than 100 flexible sigmoidoscopy screenings were excluded.

Results: Four studies were eligible (total n = 459,814). They were similar for patients' age (50-74 years), length of follow-up (11.2-11.9 years), and relative risk for colorectal cancer related mortality (0.69-0.78 with flexible sigmoidoscopy screening). For every 1000 people screened at five and 10 years, 0.3 and 1.2 colorectal cancer related deaths, respectively, were prevented. It took 4.3 years (95% confidence interval 2.8 to 5.8) to observe an absolute risk reduction of 0.0002 (one colorectal cancer related death prevented for every 5000 flexible sigmoidoscopy screenings). It took 9.4 years (7.6 to 11.3) to observe an absolute risk reduction of 0.001 (one colorectal cancer related death prevented for every 1000 flexible sigmoidoscopy screenings).

Conclusion: Our findings suggest that screening flexible sigmoidoscopy is most appropriate for older adults with a life expectancy greater than approximately 10 years.

Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.


Pooled mortality curves for colorectal cancer. Values are number of deaths from colorectal cancer prevented per 1000 people screened (absolute risk reduction). *P<0.05.

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