Changes in breast cancer mortality in Navarre (Spain) after introduction of a screening programme

Objective: The aim of this study was to assess changes in the trend of breast cancer mortality in Navarre, and the effect that a screening programme may have had on these changes. Methods: A breast cancer screening programme targeting women aged 45-65 years was launched in Navarre in September 1990. Breast cancer deaths between 1975 and 2004 were identified from the Navarre Mortality Registry, and the date of diagnosis was obtained by linkage with the population-based Navarre Cancer Registry. We compared breast cancer mortality during the pre-screening (1987-89) and screening (2002-04) periods, and with the estimated rate in the last period calculated by a linear model with a Poisson distribution. The long-term trends (from 1975 through 2004) were described by joinpoint regression analysis. Prevalent cases (those diagnosed before 1991) were excluded to minimize dilution of the benefit in the post-screening period due to deaths from tumours diagnosed before screening began. Results: The joinpoint analysis showed a rising trend in breast cancer mortality rates until 1994, followed by a continual decrease of just over 5% per year. A comparison of mortality rates between the last pre-screening and the screening periods showed a decrease of 36% (95% confidence interval [CI] 21-48%), with the largest reduction in the 50-69 years age group (52%; CI: 33-65%). In this age group, mortality in the 2002-04 period was 62% lower than that projected from extrapolation of the pre-screening trend, while in unscreened age groups (30-44 and ≥75 years), mortality was only 22% lower. When prevalent tumours were excluded, the 50-69 years age group presented a further decrease in mortality than when all tumours were considered. Conclusions: Fourteen years after the introduction of a screening programme, a major reduction in breast cancer mortality has been observed.