HDAC9 and breast cancer: To verify the epigenetic roles on ERα expression, a combination study was performed by using two important epigenetic agents including the histone deacetylase (HDAC) inhibitor, trichostatin A (TSA), and a demethylation agent, 5-aza-2'-deoxycytidine (5-aza), with EGCG treatment in ERα-negative MDA-MB-231 breast cancer cells.