NIMG-65EVALUATION OF THE TREATMENT RESPONSE OF MALIGNANT GLIOMA ON BEVACIZUMAB THERAPY USING 11C-METHIONINE POSITRON EMISSION TOMOGRAPHY

Abstract

BACKGROUND: Although anti-angiogenic therapy using bevacizumab (BEV) can induce normalization of the blood brain barrier, its effect on tumor biological activity is not well understood. We used 11C-methionine positron emission tomography (MET-PET), to evaluate biological response to BEV in patients with malignant glioma. METHODS: 8 malignant glioma patients (anaplastic oligodendroglioma 1, anaplastic astrocytoma 2, glioblastoma5) were treated with BEV (Avastin) at the time of tumor enlargement or recurrence after surgery, radiation therapy and temozolomide treatment. After initiation of BEV, they were monitored with magnetic resonance imaging (MRI) and MET-PET. MRI treatment response was evaluated according to RANO (Response Assessment in Neuro-Oncology) criteria. Methionine uptake into the tumor was expressed as a ratio to contralateral healthy brain tissue (T/N ratio). RESULTS: MRI revealed that the size of contrast-enhanced tumor was reduced and peri-tumoral edema was diminished after the initiation of BEV in all 8 cases. MRI showed a complete response according to RANO criteria in 6 of the 8 patients (75%) and a partial response in 2 patients (25%). In the contrast-enhanced tumor lesion, T/N ratio on PET decreased after initiation of BEV. In the non-enhancing tumor lesion, T/N ratio on PET after BEV was almost no difference between that before BEV. CONCLUSIONS: Our results indicate that initiation of BEV may suppress biological activity of the contrast-enhanced tumor in addition to reduce vascular permeability by restoring the blood-brain barrier. Met-PET could give us important information to understand the therapeutic mechanisms of BEV in malignant glioma patients.