Time lag to benefit after screening for breast and colorectal cancer: meta-analysis of survival data from the United States, Sweden, United Kingdom, and Denmark

OBJECTIVES To determine a pooled, quantitative estimate of the length of time needed after breast or colorectal cancer screening before a survival benefit is observed. DESIGN Meta-analysis of survival data from population based, randomized controlled trials comparing populations screened and not screened for breast or colorectal cancer. Trials were identified as high quality by reviews from the Cochrane Collaboration and United States Preventive Services Task Force. SETTING Trials undertaken in the United States, Denmark, United Kingdom, and Sweden. POPULATION Screened patients older than 40 years. PRIMARY OUTCOME MEASURES Time to death from breast or colorectal cancer in screened and control populations. INTERVENTIONS Fecal occult blood testing for colorectal cancer screening, mammography for breast cancer screening. RESULTS Our study included five and four eligible trials of breast and colorectal cancer screening, respectively. For breast cancer screening, 3.0 years (95% confidence interval 1.1 to 6.3) passed before one death from breast cancer was prevented for every 5000 women screened. On average across included studies, it took 10.7 years (4.4 to 21.6) before one death from breast cancer was prevented for 1000 women screened. For colorectal cancer screening, 4.8 years (2.0 to 9.7) passed before one death from colorectal cancer was prevented for 5000 patients screened. On average across included studies, it took 10.3 years (6.0 to 16.4) before one death from colorectal cancer was prevented for 1000 patients screened. CONCLUSIONS Our results suggest that screening for breast and colorectal cancer is most appropriate for patients with a life expectancy greater than 10 years. Incorporating time lag estimates into screening guidelines would encourage a more explicit consideration of the risks and benefits of screening for breast and colorectal cancer.