This open-label, multicenter study will evaluate the safety and efficacy of RO5323441 in combination with Avastin (bevacizumab) in patients with recurrent glioblastoma. In the dose-finding part, patients will receive intravenous escalating doses of RO5323441 in combination with 10 mg/kg Avastin once every two weeks. In the efficacy-finding part, patients will be randomized to receive the established dose (from the dose-finding part) of RO5323441 plus Avastin or Avastin alone. Patients in the dose-finding part may continue treatment with RO5323441 and Avastin on the study until evidence of progressive disease or unacceptable adverse events happen. In the efficacy-finding part, patients will receive study treatment until disease progression or death.

Inclusion Criteria:

• Adult patients, >/=18 years of age
• Histologically confirmed glioblastoma
• Radiographic demonstration of disease progression by Response Assessment in Neurooncology (RANO) criteria following prior therapy
• Availability of at least 1 formalin-fixed paraffin-embedded tumor tissue sample
• If receiving corticosteroids, patients must have been on a stable or decreasing dose of corticosteroids
• Prior standard radiotherapy for glioblastoma
• Karnofsky Performance status >/=70
• Over 4 weeks since prior surgical resection
• Over 12 weeks from radiotherapy
• Over 4 weeks from anticancer agents

Exclusion Criteria:

• Patients had second or later glioblastoma relapse
• Patients received more than one systemic treatment regimen for glioblastoma
• Patients have secondary glioblastoma
• Prior treatment with Avastin
• Patients unable to undergo Magnetic Resonance Imaging (MRI)