DLL4 and neoplasm: Finally, immunoPET targeting other overexpressed biomarkers responsible for tumor development or progression are also under investigation in gliomas, including RTKs [ephrin receptor A2 (EphA2) (395) and EGFR (396–400)], stem cell marker, CD133 (401), fibroblast activation factor-alpha (FAP-α) (402), Delta-like ligand 4 (Dll4, which is a ligand for a membrane receptor in different signaling pathways) (58), HGF (244), and MMP (403).