NI-73 * MONITORING OF BIOLOGICAL RESPONSE TO BEVACIZUMAB IN MALIGNANT GLIOMA PATIENTS BASED ON L-[methyl-11C] METHIONINE-POSITRON EMISSION TOMOGRAPHY

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 L-[methyl-11C] methionine-positron emission tomography (met-PET), to monitor the biological response to BEV in malignant glioma patients. METHODS: 5 malignant glioma patients (anaplastic oligodendroglioma 1, glioblastoma 3, gliosarcoma 1) were treated with BEV (Avastin) at the time of recurrence after surgery, radiation therapy and Temozolomide treatment. After initiation of BEV, they were monitored with magnetic resonance imaging (MRI) and met-PET. RESULT: MRI reveled that the size of contrast-enhanced tumor was reduced and peritumoral edema was diminished after the initiation of BEV in all 5 cases. In these contrast-enhanced tumor lesion, methionine uptake on PET was decreased after initiation of BEV. In the non-enhancing lesion, methionine uptake was not changed before and after initiation of BEV. CONCLUSION: Our results indicate that initiation of BEV is related not only to the effect on vascular permeability reduction by repairing the blood-brain barrier, but also to the effect on suppression of biological activity of the tumor for the contrast-enhanced lesion. On the contrary, tumor biological activity was not changed in the non-enhancing lesion. Met-PET could give us important information to understand the therapeutic mechanisms of BEV.