NI-11 PATHOLOGICAL ASSESSMENT IN THE IMPACT OF ONE-SHOT BEVACIZUMAB ON UPTAKE OF (11)C-METHIONINE

BACKGROUND: This study aimed to clarify how one-time administration of bevacizumab (BEV) changes histological features in glioblastoma, and how histological changes affect the uptake of 11C-methyl-L-methionine (11C-met) as an amino-acid tracer. MATERIALS AND METHODS: Subjects were 18 patients with newly diagnosed glioblastoma who were assigned to 2 groups: BEV group, single intravenous administration of BEV before surgical tumor removal; and control group, surgical tumor removal alone. After surgery, we compared the densities of tumor cells and microvessels, and microvascular structures including vascular pericytes and L-type amino acid transporter-1 (LAT1), between the BEV and control groups. Correlations between 11C-met uptake on positron emission tomography before surgery, microvascular density, and LAT1 expression were assessed in each group. RESULTS: BEV induced significant reductions in microvascular density, while tumor cell density and proliferation were retained in the BEV group. Percentages of vessels with pericytes and vascular endothelium with LAT1 expression were lower in the BEV group than in controls. Uptake of 11C-met correlated significantly with microvascular density in the BEV group, but not with LAT1expression. CONCLUSIONS: The present study showed that even one course of BEV administration induced reductions in microvessels, vascular pericytes, and LAT1 expression in glioblastomas. One course of BEV therapy also reduced 11C-met uptake, which might have been largely attributed to reductions in microvessels rather than reductions in LAT1 expression, in addition to reduction of vascular permeability.