Objective: Analysing trends in population breast cancer mortality statistics appears a simple method of estimating the effectiveness of mammographic screening programmes. We reviewed such studies of population-based screening in Europe to assess their value.
Methods: A literature review identified 17 papers, of which 12 provided quantitative estimates of the impact of screening. Due to differences in comparisons and outcome measures, no pooled estimate of effectiveness was calculated.
Results: Comparisons included breast cancer mortality before and after the introduction of screening, trends in early and late starting areas and trends in age groups affected and unaffected by screening. Studies that calculated the percentage annual change after the start of screening found reductions of 1-9% per year (1%, 2.3-2.8% and 9% for those with adequate follow-up). Of studies that compared mortality in time periods before and after introduction of screening, three single country studies all had adequate follow-up and estimated mortality reductions ranging from 28% to 36%. Limitations of studies of population mortality rates include the inability to exclude deaths in women with breast cancer diagnosed before invitation to screening, diluting any observable impact of screening, and the gradual implementation of screening in a country or region.
Conclusions: Although analysing population breast cancer mortality rates over time can be a first step in examining changes following the introduction of screening, this method is of limited value for assessment of screening impact. Other methods and individual data are necessary to properly quantify the effect.