This is an adaptive, randomized controlled, Phase 3 clinical trial in adult patients with histologically confirmed diagnosis of a recurrent glioblastoma multiforme (GBM) or gliosarcoma (GS), who have been previously treated with surgery (if appropriate), standard of care chemo-radiation with temozolomide, +/- adjuvant temozolomide, and bevacizumab and now have progressive disease during or after bevacizumab. Patients with prior low-grade glioma or anaplastic glioma are eligible, if histologic assessment demonstrates transformation to GBM or GS.