ESR1 and breast cancer: Though GDC-0810 clearly shares features with fulvestrant, such as the ability to down-regulate ER protein levels in breast cancer cells, the GDC-0810:ER complex interacts with a set of peptides that are distinct from those that interact with the fulvestrant:ER complex, suggesting that these compounds promote distinct ER conformations, and may therefore have a different mechanism by which they induce ER turnover.