VAV1 and breast neoplasm: At variance with other solid tumors, in which the malignancy-associated role of Vav1 has been variously linked to its GEF activity [8, 11, 13], opposite effects for Vav1 on Rac1 activation were reported in AU565 and MCF7 breast tumor-derived cell lines, also in the presence of cytoskeleton changes [14].