The effect of service screening on breast cancer mortality rates

The aim of the study was to estimate the effect of breast screening on routinely collected age-specific breast cancer mortality rates. The relative protection obtained from randomized controlled trials of screening was assigned to a time before diagnosis for women who died of breast cancer to estimate the expected number of deaths that would have been preventable if screening had occurred. Simulation was used to obtain confidence intervals for these estimates. The reduction in age-specific breast cancer mortality rates that can be expected from service screening was also estimated. The reduction in breast cancer mortality was less than that attained in most screening trials except for the 65 to 69-year age group for which the range of expected values was 21.7-24.2%. On average, breast screening from the age of 50 to 69 years reduced the overall number of deaths from breast cancer by 5.7-8.0%. Screening starting at 40 or 45 years of age with a 10-year delay in effect compared with starting at 50 years of age produced a modest reduction in breast cancer mortality. When there was, however, only a 5-year delay in effect from screening younger women the overall effectiveness of screening was greater and more dependent on the age of initial screening with a maximum reduction of 10.6% (95% CI: 8.2-12.1%) in the overall number of deaths from breast cancer. Reductions in the breast cancer mortality rates for women at 60-64, 65-69, and 70-74 years of age provide a simple measure of the effectiveness of breast screening. The percentage reduction in breast cancer mortality rates will not be as great as the reduction observed in screening trials but will be greatest for breast cancer mortality in those between the ages of 65-69 years.