ESR1 and breast cancer: FASN inhibition can mediate opposing effects on the E2/ERα-related conflicting cellular responses driven by the MAPK/ERK and PI3K/AKT pathways by switching the balance toward MAPK/ERK activation, inducing cell cycle inhibiting genes such as p21WAF1/CIP1 and p27Kip1, while suppressing PI3K/AKT-mediated cell cycle progression and cell survival, synergistically leading to suppression of E2-promoted anchorage-dependent and -independent cell growth in hormone-dependent breast cancer cells.