Breast-Cancer Tumor Size, Overdiagnosis, and Mammography Screening Effectiveness

Abstract Background The goal of screening mammography is to detect small malignant tumors before they grow large enough to cause symptoms. Effective screening should therefore lead to the detection of a greater number of small tumors, followed by fewer large tumors over time. Methods We used data from the Surveillance, Epidemiology, and End Results (SEER) program, 1975 through 2012, to calculate thetumor-size distribution and size-specific incidence of breast cancer among women 40 years of age or older. We then calculated the size-specific cancer case fatality rate for two time periods: a baseline period before the implementation of widespread screening mammography (1975 through 1979) and a period encompassing the most recent years for which 10 years of follow-up data were available (2000 through 2002). Results After the advent of screening mammography, the proportion of detected breast tumors that were small (invasive tumors measuring