NRP1 and neoplasm: This is because integrin αvβ3 is highly expressed on the surface of tumor neovascular endothelial cells and 4T1 tumor cells but not in normal tissues, which enables better accumulation of iRGD in tumor tissues in vivo (Xin et al., 2016), whereas iRGE only targets tumor tissues via the CendR pathway through NRP-1, which is expressed both in tumor cells and normal tissues (Mamluk et al., 2002; Gu et al., 2003; Ellis 2006).