ESR1 and breast cancer: To investigate whether FDY003 exerts therapeutic effects on BC cells, we treated MCF-7 (an estrogen receptor-positive human BC cell line), MDA-MB-453 (a human epidermal growth factor receptor 2- (HER2-) positive human BC cell line), and MDA-MB-231 (a triple-negative human BC cell line) cells with FDY003 for 72 h and observed their responses.