Hearing improvement after bevacizumab in patients with neurofibromatosis type 2

Abstract

Background: Profound hearing loss is a serious complication of neurofibromatosis type 2, a genetic condition associated with bilateral vestibular schwannomas, benign tumors that arise from the eighth cranial nerve. There is no medical treatment for such tumors.

Methods: We determined the expression pattern of vascular endothelial growth factor (VEGF) and three of its receptors, VEGFR-2, neuropilin-1, and neuropilin-2, in paraffin-embedded samples from 21 vestibular schwannomas associated with neurofibromatosis type 2 and from 22 sporadic schwannomas. Ten consecutive patients with neurofibromatosis type 2 and progressive vestibular schwannomas who were not candidates for standard treatment were treated with bevacizumab, an anti-VEGF monoclonal antibody. An imaging response was defined as a decrease of at least 20% in tumor volume, as compared with baseline. A hearing response was defined as a significant increase in the word-recognition score, as compared with baseline.

Results: VEGF was expressed in 100% of vestibular schwannomas and VEGFR-2 in 32% of tumor vessels on immunohistochemical analysis. Before treatment, the median annual volumetric growth rate for 10 index tumors was 62%. After bevacizumab treatment in the 10 patients, tumors shrank in 9 patients, and 6 patients had an imaging response, which was maintained in 4 patients during 11 to 16 months of follow-up. The median best response to treatment was a volumetric reduction of 26%. Three patients were not eligible for a hearing response; of the remaining seven patients, four had a hearing response, two had stable hearing, and one had progressive hearing loss. There were 21 adverse events of grade 1 or 2.

Conclusions: VEGF blockade with bevacizumab improved hearing in some, but not all, patients with neurofibromatosis type 2 and was associated with a reduction in the volume of most growing vestibular schwannomas.

Figure 1. Angiogenic Profile of Vestibular Schwannomas

Panel A shows immunohistochemical analysis of members of the vascular endothelial growth factor (VEGF) pathway in normal peripheral nerve and schwannoma. In normal nerve, staining for VEGF highlights Schwann cells (arrows), and staining for VEGF receptor 2 (VEGFR-2) highlights vessels (arrowheads). Staining for neuropilin-2 (NRP-2) and semaphorin 3F (SEMA-3F) highlights Schwann cells in normal nerve. In schwannomas, VEGF staining highlights tumor cells (arrowhead) and blood vessels (arrow); VEGFR-2 staining highlights some vessels (arrowheads), whereas others remain unstained (arrows). Tumor cells stain diffusely for NRP-2 but not for SEMA-3F. In all panels, brown staining shows positivity for the given antigen, and blue labels the nuclei, with the letter A denoting axon, the letter M myelin, and the letter S Schwann cell. Panel B shows the percentage of samples with expression of more than 1 on a scale of 0 (no staining) to 3 (strong staining) for the known members of the VEGF pathway (ligands and receptors). SEMA-3F and SEMA-3A are expressed in all nerve roots (3 intensity). In samples from patients with neurofibromatosis type 2 (NF2), 58% of the tumors have completely negative staining for SEMA-3F, and 22% are negative for SEMA-3A. In samples from patients with sporadic tumors, 44% of tumors are negative for SEMA-3F, and 33% are negative for SEMA-3A. Since none of the samples were scored as 2 or 3, no bar is shown for SEMA-3A. Panel C shows the quantification of the number of vessels per square millimeter expressing VEGFR-2 and NRP-2 in vestibular schwannomas associated with neurofibromatosis type 2 and sporadic vestibular schwannomas. CD31 was used to count the total number of vessels per square millimeter. There were no significant differences between tumors associated with neurofibromatosis type 2 and sporadic tumors. Panel D shows statistical analysis of the morphometric measures. Diameter, perimeter, and microvascular density were all significantly smaller for the 470 vessels analyzed in normal peripheral nerve roots than in either schwannomas associated with neurofibromatosis type 2 (1215 vessels from 20 patients) or sporadic schwannomas (2104 vessels from 17 patients). The perimeters (or surface area, data not shown) were significantly larger in tumors associated with neurofibromatosis type 2 than in sporadic tumors.

Figure 2. Changes in Magnetic Resonance Imaging (MRI) Measures during Treatment with Bevacizumab

Panel A shows the correlation between mean apparent diffusion coefficients (ADCs) at baseline and subsequent changes in tumor volume for the 10 patients after 3 months of treatment with bevacizumab. Panel B shows dynamic contrast-enhanced MRIs of Patient 6, with measures of blood flow and vascular permeability indicating the permeability of vestibular schwannomas (with the most permeable areas shown in white and the least permeable areas in dark red). At baseline, permeability is high for both tumors but decreases progressively during 12 months of treatment, as shown by the values beneath the images. Panel C shows representative cranial T₁-weighted MRI scans of Patient 2 after the administration of contrast material at baseline (left) and after 9 months of treatment (right). T₂-weighted scans are also shown at the same time points. The overall decrease in tumor volume (30%) can be seen by comparing the tumor outline at baseline (yellow line) with the outline after 3 months of treatment with bevacizumab (red line). The enhancement pattern in vestibular schwannomas did not change noticeably during treatment with bevacizumab.