A large study from Sweden suggests that mammographic screening for breast cancer reduces the risk of death from breast cancer by 40%-45%. These results were published in the journal Cancer Epidemiology Biomarkers & Prevention.
Breast cancer is diagnosed in approximately 250,000 women each year in the U.S. alone. Since the disease is highly curable when it is found and treated early, it is recommended that women 40 years of age or older undergo screening mammography every 1-2 years.
To evaluate the effect of screening mammography on breast cancer mortality, researchers conducted a study among women living in nine counties in Sweden. The study participants represented roughly 45% of the total female population of Sweden. Though a previous report by these researchers demonstrated that mammographic screening reduced breast cancer mortality, the current study differed in that it involved a larger number of women and a longer period of follow-up.
To estimate the benefit from screening mammography, researchers compared mortality rates during two time periods-the period prior to the introduction of screening and the period after the introduction of screening. Information was available for 542,187 women during the prescreening period and for 566,423 women during the screening period.
Roughly 75% of women participated in the screening program. During 22 to 44 years of follow-up, there were a total of 6,231 deaths due to breast cancer; 4,778 of these occurred among women who had been initially diagnosed with breast cancer during the study period.
Compared with the prescreening period, breast cancer mortality rates were 45% lower after introduction of the screening program. After accounting for factors that may bias study results, there was still a 43% reduction in breast cancer mortality in the screening period. These findings indicate that an estimated 472 women would need to be screened in order to save one life.
The researchers conclude that these results provide further evidence that screening mammography reduces the risk of death from breast cancer.
Reference: The Swedish Organised Service Screening Evaluation Group. Reduction in Breast Cancer Mortality from Organized Service Screening with Mammography: 1. Further Confirmation with Extended Data. Cancer Epidemiology Biomarkers & Prevention. 2006;15:45-51.