GSA-Tumor allows division of the 1881-sample data set into five major subgroups based on clinical annotations available from GEO [13]; 1) all 1881 tumors, 2) ER-positive tumors (n = 1225), 3) ER-negative tumors (n = 395), 4) systemically untreated patients (n = 927), and 5) patients treated with tamoxifen alone (n = 326, GSE6532 [27] and GSE12093 [28]). This evidence concerns the gene ESR1 and neoplasm.