AZD9496 showed pmol/L equipotent binding to both ERα and ERβ isoforms. AZD9496 directly targets ERα for downregulation in vitro. And it also antagonizes and downregulates mutant ER in vitro and in vivo. The IC50s of ERα binding, ERα downregulation, ERα antagonism for AZD9496 are 0.82, 0.14 and 0.28 nM, respectively.