ESR1 and breast cancer: To investigate the relation between FOXC1 and ERα in the growth of breast cancer cells, MCF‐7 vector and MCF‐7‐FOXC1, T47D vector and T47D‐FOXC1, BT549 vector and BT549 FOXC1 shRNA, HCC1806 vector and HCC1806 FOXC1 shRNA cells were cultured in DMEM (without phenol red) with E2 or normal culture medium.