CD44 and glioblastoma: While biomarkers used for the diagnosis of GBM, such as TERT (telomerase reverse transcriptase) [18], MGMT (O-6-Methylguanine-DNA Methyltransferase) [19], CD44 [20], ATRX (alpha-thalassemia/mental retardation, X-linked) [21], MMP9 (matrix metallopeptidase 9) [22], TNF-alpha (tumor necrosis factor-alpha) [23], S100A8 (S100 Calcium Binding Protein A8) [24], MCT1 (Monocarboxylate transporter 1) [25], and thrombospondin-1[26] can predict the prognosis in glioblastoma patients, it is difficult to predict the clinical outcome after anti-angiogenic treatment using those biomarkers.