While the accumulating evidence points to tumor suppressor functions of GATA3, in luminal breast cancer GATA3 directly upregulates proto-oncogenes [1],[18]-[20], including the alpha subunit of ER (ERα) and co-regulates a large set of ERα target genes, suggesting that, contrary to the basal-like associated behavior, GATA3 may promote tumorigenesis in luminal breast cancer, either through ER dependent processes, or possibly, independent of ER. This evidence concerns the gene ESR1 and breast cancer.