The Swedish Randomised Mammography Screening Trials: Analysis of Their Effect on the Breast Cancer Related Excess Mortality

Objective –To apply an indirect method for estimation of the breast cancer related excess mortality in the Swedish randomised mammography screening trials. Setting –Randomised trials on mammography screening have, in Sweden, been performed in the counties of Kopparberg (W) and Östergötland (E), the so called WE study, and in the three largest cities in Sweden, Stockholm (southern part), Gothenburg, and Malmö. An overview of the trials was presented in the Lancet in 1993 and included 156 911 women in the invited group and 125 866 in the control group. Methods –The excess mortality in the breast cancer subgroups was estimated by indirect standardisation using official national cause of death statistics according to Statistics Sweden as a reference. Results—The estimated reduction of the breast cancer related mortality was 24% for the whole group (40–74 years at randomisation). The corresponding figures for the age groups 40–49, 50–59, and 60–69 years were 6%, 28%, and 34% respectively. Conclusion –The results are very similar to those presented earlier based on the traditional comparison of the breast cancer mortality in the invited and in the control group. This analysis further strengthens previous reports on a beneficial effect of mammography screening, which is especially pronounced in the age group 50–69.