Time trends of breast cancer mortality in Spain during the period 1977-2001 and Bayesian approach for projections during 2002-2016

Background: In recent decades, changes in breast cancer (BC) mortality trends have been observed across Europe. Our objective is to describe BC mortality trend in Spain during 1977-2001 and to estimate BC mortality projection in the period 2002-2016 using a Bayesian approach. Material and methods: An age-period-cohort (APC) analysis has been carried out in order to investigate the effect of the age, period and birth cohort on BC mortality in Spain during 1977-2001 and to estimate future trends for the period 2002-2016. A Bayesian APC model with an autoregressive structure for the age parameters has been used for projections of BC mortality. Results: BC mortality rates increased 2.18% per year during 1977-1991 followed by a significant fall after 1992 (estimated annual percent change = -2.67%; 95% confidence interval = -2.97, -2.31). Cohorts born before 1952 showed higher risk of death from BC than those born after this year. Projections showed an increase of mortality among women older than 50 years in the period 2002-2016 (range of increase = 10%-40%). Conclusions: The decrease of BC mortality since 1992 could be attributable to BC down-staging due to early detection and effectiveness of cancer treatment. The effect of ageing on the female population, immigration and the increase of BC incidence observed in Spain could explain the increase in BC mortality predicted for the years to come among women older than 50 years. BC screening to the whole Spanish population and new treatments introduced in the last few years could modify the predictions of BC mortality. Future forecasting studies should be carried out considering these new factors in the natural history of BC in Spain.