The Effect of Bevacizumab on Vestibular Schwannoma Related to Neurofibromatosis Type 2

Introduction: We describe an Australian experience of infusional bevacizumab for vestibular schwannoma (VS) in neurofibromatosis type 2 patients, with specific focus on 3-dimensional tumour volume and audiometry. Method: Data was pooled from patients with symptomatic or progressive VS from 2009 to April 2018. Tumours were assessed as total volume per patient. Bevacizumab infusions were administered every 2-4 weeks. 3-D volumetric response (cm 3 ) was determined through serial magnetic resonance imaging, at baseline and at 3-6-month intervals, until cessation of infusions following progression or prior to surgery. Volumetric response was defined as a reduction of volume ³ 20%, from baseline. Patients underwent interval pure tone audiometry. A decrease in the average pure tone analyses by 10dB indicated response. Results: Twenty-one VS tumours were identified in eleven patients. Median age was 26 (range 13 – 67yr). Average baseline tumour volume was 14.17cm 3 (range 1.45cm 3 - 38.51cm 3 ). Tumour volume reduction >20% was shown in 7/11 patients (64%), indicating partial response, 2/11 (18%) patients showed stable disease, and 2/11 (18%) progressed. Average percentage tumour volume change was +4.45% from baseline (range -57% to 241%). 16 individual ears were tested, 3/16 (19%) of ears showed an average decibel reduction of 10dB or more, indicating response (average change 2.5dB, range -36dB to 81dB). 10/16 (63%) showed stable hearing, and 3/16 (19%) showed hearing deterioration. Conclusion: Bevacizumab is a useful agent for reducing tumour volume and improving hearing losses due to vestibular schwannoma in neurofibromatosis type 2 patients. These results reflect results described from the United Kingdom and United States.