The GSE3494 data set consists of microarray gene expression data for ER-positive and ER-negative breast tumors including histological grade 2 and 3 tumors in both ER classes and the GSE5460 data set consists of data for HER2-positive and HER2-negative breast tumors including histological grade 2 and 3 tumors in both HER2 classes. This evidence concerns the gene ESR1 and breast neoplasm.