Breast cancer mortality in Barcelona following implementation of a city breast cancer-screening program.

Background: To assess the impact that the Barcelona city breast cancer-screening program has had in the decline of mortality due to breast cancer among women aged 50-74 years, in the city of Barcelona.

Methods: A quasi-experimental study based on breast cancer deaths among women aged between 50 and 74 years residing in Barcelona between 1984 and 2004. The variables used were: age, year, and Primary Health Care District (ABS) grouped into four zones according to the year of implementation of the screening program. We carried out a descriptive analysis of mortality by year and age and fitted Poisson models to calculate the relative risk of dying prior to the existence of the program, after its implementation, and as a function of its degree of implementation. The models are adjusted for ABS socioeconomic level.

Results: Between 1984 and 2004, 3733 women aged between 50 and 74 years died of breast cancer. The mortality rate fluctuated, reaching its highest level in 1991, having declined since. Prior to implementation of the program, mortality was falling by 1% annually (RR=0.99 95 CI%=0.98-0.99), and since then by 5% (RR=0.95 95 CI%=0.92-0.99). There are no significant differences in mortality reduction between zones where the program was implemented earlier and those where it came in later, even though mortality in the final phase of complete implementation is significantly lower by 17%, with respect to the period prior to its introduction.

Conclusions: The results show a reduction in mortality due to breast cancer over the entire period studied, the decline being more marked after the program was introduced. Opportunistic screening and the greater efficacy of the treatment of initial cancers have both influenced the findings. A longer follow up time will be needed in order to obtain more conclusive results.