ESR1 and breast cancer: Figure 4 depicts the mechanism of action of the ER ligands at the ERα level. E2, TAM, and ICI 164,384 (ICI) bind to ER LBD, which explains why they compete with E2 at the ERα level and can inhibit E2-mediated BC cell proliferation. TAM might exert its antiproliferative potency through other ER-dependent mitogenic pathways [33,34,35,36,37].