“…Therefore, many of the selected studies used human U87-MG tumor cells [ 32 , 34 , 38 , 52 , 53 , 55 , 56 , 57 , 58 , 59 , 62 , 63 , 64 , 66 , 67 ], in which the tumor has a diffusely invasive infiltration pattern into normal brain parenchyma, resistance to therapy, and high recurrence rate [ 70 ]. Studies also used rat C6 tumor cells [ 41 , 51 , 54 , 60 , 61 ], in which the tumor mimics several features of human GBM including a high mitotic index, focal tumor necrosis, parenchymal invasion, and neoangiogenesis [ 71 , 72 ]. The GBM orthotopic model was induced mainly in immunosuppressed animals (e.g., nude or SCID ) because this immunodeficient condition allows a greater possibility of the growth of human (xenogeneic) tumor cells after implantation, preventing their rejection [ 73 ].…”