A gene expression signature of E2 treatment is associated with ER-positive breast cancer. The degree of association with the E2 treatment signature (SA score) is significantly higher in ER-positive (dark green) than in ER-negative (light green) primary breast tumors [34, 53–55] or cell lines. ER status of tumors was extracted from sample annotation provided by each dataset; ER status of cell lines was obtained from the American Type Culture Collection (ATCC) or prior reports [56–61]. Cell lines EVSA-T and UACC-812 were removed from analysis due to conflicting reports regarding ER status. Cell lines MDA-MB-435 and MT-3 were removed from analysis as they have been shown to be cross-contaminated with melanoma and colon cancer cell lines, respectively [62, 63]. Heavy lines and shaded boxes indicate the median and interquartile range (IQR) of the SA scores of each group, respectively. Dashed lines extend to the most extreme data points within 1.5 * IQR of the shaded box. Points outside the dashed lines are plotted as open circles. All p values were computed using Welch's t test.