RAC1 and neoplasm: By in vitro cell and in vivo animal approaches, we have demonstrated that Rac1 possibly through VEGF/VEGFRs/PI3Kβ /Rac1/ROS signaling cascade mediates endothelial permeability and transendothelial passage of tumor cells in response to tumor-derived VEGF, and that knockdown of endothelial Rac1 attenuates hematogenous metastasis of tumor cells to lungs.