KDR and neoplasm: The low-density subpopulations at these time points correspond to moderately low surface-VEGFR2: At week 3, ∼30% of the tumor cells have 3000 VEGFR2 on the tumor plasma membrane (Fig. 5B), while at week 6, 49% have only 1600 VEGFR2 on the cell surface (Fig. 5D).