Mammography Screening and Breast Cancer Mortality in Sweden

Swedish women aged 4069 years were gradually offered regular mammography screening since 1974, and nationwide coverage was achieved in 1997. We hypothesized that this gradual implementation of breast cancer screening would be reflected in county-specific mortality patterns during the last 20 years. Using data from the Swedish Board of Health and Welfare from 1960 to 2009, we used joinpoint regression to analyze breast cancer mortality trends in women aged 40 years and older (1286000 women in 19951996). Poisson regression models were used to compare observed mortality trends with expected trends if screening had resulted in breast cancer mortality reductions of 10%, 20%, or 30% among women screened during 18 years of follow-up after the introduction of screening. All statistical tests were two-sided. From 1972 to 2009, breast cancer mortality rates in Swedish women aged 40 years and older declined by 0.98% annually, from 68.4 to 42.8 per 100000, and it continuously declined in 14 of the 21 Swedish counties. In three counties, breast cancer mortality declined sharply during or soon after the implementation of screening; in two counties, a steep decline started at least 5 years after screening was introduced; and in two counties, breast cancer mortality increased after screening started. In counties in which screening started in 19741978, mortality trends during the next 18 years were similar to those before screening started, and in counties in which screening started in 19861987, mortality increased by approximately 12% (P = .007) after the introduction of screening compared with previous trends. In counties in which screening started in 19871988 and in 19891990, mortality declined by approximately 5% (P = .001) and 8% (P < .001), respectively, after the introduction of screening. County-specific mortality statistics in Sweden are consistent with studies that have reported limited or no impact of screening on mortality from breast cancer.