Effect of Screening Mammography on Breast Cancer Detection and Mortality

This widely discussed study by Bleyer and Welch published in The New England Journal of Medicine (NEJM) “The Effects of Three Decades of Screening Mammography on Breast Cancer Incidence” concluded that screening mammography leads to a substantial overdiagnosis of early breast cancer (estimated 69% increase) while only having a small effect on late-stage breast cancer (estimated 8% decrease). In a population-based observational study, the authors utilized trend data from the Surveillance, Epidemiology and End Results (SEER) database to examine trends on the incidence and stage of early- versus late-stage breast cancer at the time of diagnosis. They compared 2 time frames: prior to widespread mammography screening (1976–1978) and after mammography screening was introduced in the United States (2006––2008). This article reviews this NEJM article and describes several methodological assumptions by the authors that have been soundly criticized and the associated limitations. As a result of these limitations, there was an exaggeration of the overdiagnosis of early-stage disease with mammography and, more importantly, a substantial underestimate of the impact of mammography on decreasing late-stage breast cancer.