A SERD (IC50 0.138 nM for ERa downregulation) selective for ERa compared to other nuclear hormone receptors (IC50s 0.0008 0.54 0.92 and 30 M for ERa PR GR and AR respectively) decreases ERa activity (IC50 0.282 nM for PR antagonism) reduces proliferation of MCF-7 breast cancer cells (IC50 0.0398 nM) inhibits MCF-7 xenograft growth in mice in a dose-dependent manner