ESR1 and breast cancer: Correspondingly, DNA methyltranferase (DNMT) inhibitors such as 5-aza-2'-deoxycytidine (5-aza) and histone deacetylase (HDAC) inhibitors like trichostatin A (TSA) have been successfully used to induce ER expression and sensitize hormone-resistant ERα-negative breast cancer cells to chemotherapy [8,10-12].