We have previously shown that the expression of TWIST1 reprogrammed the non-metastatic, estrogen receptor α-positive (ER+) and HER2-negative (HER2−) MCF7 breast cancer cells with high-level expression of luminal epithelial genes into metastatic, ER-negative (ER−) and HER2-negative (HER2−) breast cancer cells with a more triple-negative breast cancer (TNBC)-like phenotype, as evidenced by their high-level expression of mesenchymal genes and very low level of epithelial genes [25]. Here, ESR1 is linked to breast cancer.