Lastly, while tumor angiogenesis clearly plays a role in the tumor phenotypes described in our studies, potential contributions of angiogenesis independent mechanisms such as vascular co-option, a process involving crawling along existing host vasculature by cancer cells to gain access to blood supply29, cannot be ruled out, particularly regarding the consequence of endothelial FGFR1/2 deletion. This evidence concerns the gene FGFR1 and neoplasm.