According to our aforementioned observation that EGCG combined with TSA leads to synergistic re-expression of ERα mRNA in ERα-negative breast cancer cells, we next sought to investigate whether this effect could alter ERα-dependent cellular responsiveness either to the ligand activator, 17 β-estradiol (E2), or the antagonist, tamoxifen. This evidence concerns the gene ESR1 and breast carcinoma.