ESR1 and breast cancer: SRC-1 serves as a coactivator of multiple transcription factors, such as HOXC11, PEA2, AP-1, HIF1α, c-FOS, Ets1/2, and STAT1/3, to promote the expression of oncogenes, including S100β, Twist, ITGA5, VEGFa, CSF1, and HER2, in the progression of breast cancer, and estrogen-mediated ER activation is critical (Fig. 4).