P04.22 Diffusivity changes in bevacizumab-responding and refractory meningioma

Abstract

Introduction: Meningiomas may be highly vascularized and therefore respond to antiangiogenic treatment such as bevacizumab (Bev). Here we report on the time course of diffusivity as surrogate of tumor cell density and ischemic tissue changes in a patient with multiple intra- and extracranial meningiomas WHO grade III. Tumors initially responded to Bev, but were refractory at second Bev exposure. Materials and Methods: A 73 years old patient was studied at the time of 7th tumor recurrence. Size and diffusivity (apparent diffusion coefficient, ADC) of six meningiomas were quantified using ROI analysis on gadolinium-enhanced T1-weighted and corresponding diffusion weighted MRI. Bev treatment was delivered every two weeks with a dose of 10 mg/kg per infusion. Results: Mean tumor size increased 3.5-fold during spontaneous growth over 3.5 months, which was paralleled by an ADC decrease from 750 ± 214 to 644 ± 83*10-6mm2/s (mean±SD). The first Bev treatment period led to a response of all six meningiomas and induced a peak tumor size decrease of 70% at seven months. During that period ADC values increased 1.4-fold reaching a maximum already at 2 months. After seven months Bev had to be discontinued due to limb edema and proteinuria. Without Bev tumor size again increased 2.7-fold over seven months. Therefore Bev treatment was resumed, however, during the second treatment period of 4 months tumor size further increased, but ADC values remained unchanged (mean 1030 ± 321*10-6mm2/s). DISCUSSION: Successful Bev exposure lead to an early ADC increase which may be attributed to ischemic tumor damage and a decrease of tumor cell density. Vice versa, ADC remained unchanged during Bev resistence which indicates that ADC measurement may predict antiangiogenic treatment response or failure. This issue has to be addressed in a larger study. If confirmed ADC may be used to individualize meningioma treatment with Bev.