KDR and neoplasm: To determine whether VEGFR-2 expression on pCSCs is regulated by tumor environmental cues, we examined the effects of cytokines on the expression in vitro., including Flt3 ligand (FL) [31], GM-CSF [32], IL-3 [33], IL-4 [34], IL-6 [35], IL-7 [36] and IL-13 [37].