KDR and neoplasm: Regarding the preparation of the targeted bubbles, these studies reported the usability of peptides binding to erythropoietin-producing hepatocellular receptor A2 (EphA2) on tumor cells, to the vascular endothelial growth factor receptor 2 (VEGFR2) of tumoral endothelium, or to integrin αvβ3 of endothelial cells.