L1CAM and glioblastoma: Fifth, active targeting can be achieved by attaching substances to nanoparticles that specifically target a part of GBM tumor cells [6], such as an antigen (i.e., A2B5), differentiation clusters (i.e., CD15, CD33, CD44, or CD133), receptors of cytokines (i.e., interleukin13 receptor), and several proteins (i.e., Integrin-a6, α5β3, ανβ3 or L1CAM), which are expressed in GBM cells and can promote tumorigenesis.