ESR1 and breast cancer: The proliferation of ER-positive (MCF-7) and ER-negative (MDA-MB-231) human breast cancer cells lines, which respond to physiological concentrations of E2 (1nM) was used to characterize the oestrogenic activity of ZEA and derivatives through oestrogenic parameters such as proliferative effect (PE), relative proliferative effect (RPE) and relative proliferative potency (RPP) [4].