Contribution of early detection and adjuvant treatments to breast cancer mortality reduction in Catalonia, Spain

Abstract

Background: Reductions in breast cancer (BC) mortality in Western countries have been attributed to the use of screening mammography and adjuvant treatments. The goal of this work was to analyze the contributions of both interventions to the decrease in BC mortality between 1975 and 2008 in Catalonia.

Methodology/principal findings: A stochastic model was used to quantify the contribution of each intervention. Age standardized BC mortality rates for calendar years 1975-2008 were estimated in four hypothetical scenarios: 1) Only screening, 2) Only adjuvant treatment, 3) Both interventions, and 4) No intervention. For the 30-69 age group, observed Catalan BC mortality rates per 100,000 women-year rose from 29.4 in 1975 to 38.3 in 1993, and afterwards continuously decreased to 23.2 in 2008. If neither of the two interventions had been used, in 2008 the estimated BC mortality would have been 43.5, which, compared to the observed BC mortality rate, indicates a 46.7% reduction. In 2008 the reduction attributable to screening was 20.4%, to adjuvant treatments was 15.8% and to both interventions 34.1%.

Conclusions/significance: Screening and adjuvant treatments similarly contributed to reducing BC mortality in Catalonia. Mathematical models have been useful to assess the impact of interventions addressed to reduce BC mortality that occurred over nearly the same periods.

Figure 1. BC mortality rates and screening.

Standardized BC mortality rates for the age groups: A) 30–79, B) 30–69. Observed rates (dots) and estimations under different scenarios Background (gray) and Only screening (green).

Figure 2. BC mortality rates and different scenarios.

Standardized BC mortality rates for the age group 30–69. Observed rates (dots) and estimations under different scenarios Background (gray), Only screening (green), Only adjuvant treatments (cyan), and Both interventions (magenta).

Figure 3. Sensitivity analysis.

Standardized BC mortality rates for the age group 30–69. Observed rates (dots) and estimations for All interventions scenario. A) Changing the BC survival pdfs by the US pdfs for women diagnosed since 1995. B) Changing the year of introduction of adjuvant treatments: 1975, 1990, and 1995 (from bottom to top).

Figure 4. BC mortality rates and different scenarios.

Standardized BC mortality rates for the age group 30–69. Observed rates (dots) and estimations under different scenarios Background (gray), Only screening (green), Only adjuvant treatments (cyan), Other causes (dark blue), and All interventions (magenta).