ESR1 and breast cancer: The data reveals a gradual reduction in ER-α expression from 2h to 6h in MCF7 cells (Fig 4A), while there is no detected expression in MDA-MB-231 (Fig 4B), consistent with previous studies, which demonstrate that pan-HDAC inhibitors, such as TSA and SAHA, can repress ERα expression and inhibit the growth of ER-positive breast cancer cells [25].