Inclusion criteria: Patients aged 18 or older with histological diagnosis of anaplastic astrocytoma (WHO grade III) or glioma (WHO grade IV) Assigned to bevacizumab treatment (monotherapy or adjunctive to chemotherapy) for therapeutic reasons by an oncologist Patients should be on a stable or decreasing dose of steroids Willingness and ability to comply with the protocol Patient should present with a KPS of >=70 Signed informed consent