Contrary to this a priori hypothesis, in the studies presented here, TGFβ was in fact demonstrated to be a necessary driver of ER+ breast cancer osteolytic BMET progression in an E2-dependent ER+ model where tumor-associated osteolysis and osteolytic BMET progression are also dependent on tumoral ER signaling [12]. This evidence concerns the gene TGFB1 and breast cancer.