The impact of mammographic screening on breast cancer mortality: overview of the evidence so far

Controversy remains over the scale of benefit women can expect from attending mammographic screening programs. We review the evidence, presenting (1) an updated meta-analysis of the latest results from the randomised trials and (2) an overview of the non-randomised evidence. After eight randomised trials with 12–20 years follow-up, the pooled results show a significant 20% (95% confidence interval [CI]: 14%, 27%) reduction in breast cancer mortality associated with invitation to screening. When stratified by age, the reductions were 15% (95% CI: 2%, 27%) for women aged under 50 and 22% (95% CI: 14%, 30%) for women aged 50–74. The search strategy for nonrandomised evidence relating to mortality yielded 12 descriptive studies, seven case-series, six case–control, eight cohort and three nonrandomised comparative studies. All indicated some benefit associated with screening. Overall, the case–control studies indicated a 35% (95% CI: 20%, 48%) reduction in breast cancer mortality associated with screening. The corresponding reduction for cohort studies was 44% (95% CI: 39%, 48%) for screening and 31% (95% CI: 21%, 40%) for invitation. The majority of evidence from randomised and nonrandomised sources demonstrates a reduction in breast cancer mortality with screening. Studies should continue to monitor the benefit of screening programmes, taking care to address potential forms of bias.