DLL4 and glioblastoma: These tracers target membrane proteins whose expression is altered in glioblastoma (including the EGFR, DLL4, EPHA2, CD47, AC133 antigen, and MT1-MMP) [94,95,96,97,98,99,100,101,106,107]: several components of the tumor microenvironment including vessels, macrophages, and extracellular matrix proteins [104,105,108,109,110,114].