HDAC9 and breast cancer: To determine the transcriptional regulation of CD24 expression in breast cancer cells, CD24 high-expressing MCF7 cells and CD24 low-expressing MDA-MB–231 cells were treated with epigenetic drugs, namely a DNA methyltransferase (DNMT) inhibitor (5-aza-dC) and a histone deacetylase (HDAC) inhibitor (TSA).