KDR and neoplasm: These models have been used to describe many aspects of angiogenesis, e.g., host tissue distribution of a chemotactic factor following its secretion from a tumor [16], VEGF-VEGFR interactions [17], a fibroblast growth factor-binding network [18], whole-body compartmental distribution of VEGF under exercise and peripheral artery disease conditions [19,20], the contribution of endothelial progenitor cells to circulation of VEGF in organs and their effects on tumor growth and angiogenesis [21], and a VEGF reaction-transport model in skeletal muscle [22].