GREB1 and breast cancer: Although in vitro studies in breast cancer models showed that GREB1 siRNA-mediated suppression reduced cancer cell proliferation in the presence of 17-β estradiol (a major intermediary in the development and evolution of breast cancer [19]) and that GREB1 was involved in the estrogen stimulated cell growth through the estrogen/MYC/miR-26 axis [20], to date, the evidence indicates that GREB 1 expression correlates with good prognostic outcome in breast cancer patients [13,21].