FLT1 and neoplasm: The CD11b+ cells by stimulating the versican (ECM proteoglycan) inhibit the TGF-β/Smad2 signaling pathway, promote MET, increase proliferation, and speed up metastasis.165 Both VEGFR1+ BMDC and CD11b+ secrete large amounts of MMP9, which in turn, participate in ECM and vascular remodeling, angiogenesis, and vasculogenesis.160,166 These VEGFR1+ BMDC cells directly recruit VEGFR2+ circulating endothelial progenitor cells and thereby help to vascularize the niche and promote tumor sprouting.