KDR and neoplasm: We have quantified the effect of utilizing experimental data for the density of VEGF receptors, accounting for VEGF receptors on both the abluminal and luminal endothelial surface, and including receptor expression on parenchymal cells (NRP1 on muscle fibers and VEGFR1, VEGFR2, NRP1, and NRP2 on tumor cells), as shown in Figure 2.