Glioblastoma is the most common malignant primary brain tumor with poor prognosis because of its diffusive and infiltrative nature. The FDA approved the use of the anti-VEGF antibody bevacizumab in recurrent GBM. However, resistance to this anti-angiogenic reagent is frequent and fails to enhance patients' overall survival. The investigators previously identified one novel mechanism responsible for bevacizumab-resistance in CD146-positive glioblastoma (Joshkon et al. Acta Neuropathol Commun, 2022). Now, the investigators objective is to prospectively monitor the soluble CD146 value in plasma from patients treated by bevacizumab for recurrent glioblastoma. The investigators will collect plasma at baseline, before the first bevacizumab administration, before the second administration, at the time of first MRI evaluation and at progression. Plasma CD146 value will be analyzed by ELISA. The investigators expect to confirm the correlation between soluble CD146 value in plasma and patient response to bevacizumab.