[Efficacy of mass screening for breast cancer; reduced mortality nationally and internationally].

Breast cancer screening trials in several countries have proved to reduce breast cancer mortality. However, the trials show considerable differences in the extent of this reduction. The Swedish projects in Kopparberg/Ostergötland and Malmö are the most similar to the Dutch situation. The confidence intervals of the effect estimates of both projects are large. A critical review of all differences cannot yet lead to a conclusion on the difference in the estimated effects of both trials. Assuming equal mammographic quality in both projects, a reduction of 33% in breast cancer mortality for women in the age-group of 50 to 70 years seems a good estimate for similar projects. This assumption applied to a Dutch nationwide project, it will eventually lead to a reduction in breast cancer mortality of 16% for the entire population. In the year 2015 about 700 women will not die of breast cancer who would have without screening.