PLXNB1 and neoplasm: Activation of Plexin-B1 on endothelial cells by Sema4D which is expressed by tumor cells (58), promotes angiogenesis (45, 46, 58); therefore, whole-body knockout of Plexin-B1 in our mouse models would inhibit Sema4D-induced angiogenesis and this may contribute to the decrease in metastasis observed.