KDR and neoplasm: Primary tumors depend on the VEGF-dependent recruitment of bone marrow-derived precursors (e.g., VEGFR1+ hematopoietic and VEGFR2+ circulating endothelial progenitor cells (EPCs) as a source of ECs) that initiate neovascularization (106) in response to specific TME ECM changes and the chemo-cytokine tumor- and tumor-associated stroma repertoire.