Prior to the 1980s, there were minimal differences between blacks and whites in breast cancer mortality after adjustment for differences in incidence. There also were few available breast cancer treatments other than radical surgery. Black-white mortality differences in breast cancer mortality emerged in the United States in the late 1980s, with the advent of adjuvant systemic therapies and mammography, and they persist to the present.1 These trends suggest that, unless the underlying biology of breast cancer has changed differentially by race over time, the majority of disparities are likely to be related to variations in the use and quality of screening and adjuvant treatment. Although a large body of research has sought the reasons for any such differences, most investigations have not included representative US population samples or could not quantify the separate and combined contributions of multiple factors to observed disparities.