SPP1 and neoplasm: Unmodified RGD-peptide (Arg-Gly-Asp) binds specifically to αVβ3 and αVβ5 receptors, such as fibrinogen, fibronectin, vitronectin, plasminogen, thrombospondin, prothrombin, MMP-2, laminin, osteopontin, etc. which are excessively expressed on tumor cells and surfaces of vasculature, and is applied as an important component of a delivery system of various agents: Anticancer drugs, nanoparticles, imaging compounds, and virus vectors to tumor or angiogenic vessels [65,66,67,68,69].