Sustained response to bevacizumab in a patient with mosaic neurofibromatosis type 2 carrying the NF2:c.784C>T p.(Arg262*) variant.

Neurofibromatosis type 2 (NF2) is a tumor predisposition syndrome characterized by the growth of schwannomas, especially bilateral vestibular schwannomas (VS), meningiomas, and ependymomas. The anti-VEGF antibody bevacizumab has shown efficacy for VS in some NF2 patients. However, there is limited data on the effect of bevacizumab on non-vestibular tumors, and on the correlation between therapy response and genotype. Here, we report on a 33-year-old patient with bilateral VS, 14 additional intracranial or spinal schwannomas, and a meningioma treated with bevacizumab, off-label in the European Union, for 2 years. The genotype of the patient was determined by mutational analysis of NF2, SMARCB1, and LZTR1 on DNA of multiple tissues. Additionally, we performed volumetric measurements of quantifiable non-vestibular tumors (n = 8) on MRI scans from 5 pre-therapeutic and 2 therapeutic years, and pure-tone audiometry of the non-deaf ear. A heterozygous NM_000268.3(NF2):c.784C>T p.(Arg262*) variant was identified in DNA from 3 schwannomas, but not in leukocyte or oral mucosa DNA, and no rare SMARCB1/LZTR1 variants were detected, establishing the diagnosis of definite NF2 mosaicism. While schwannomas had progressed with a mean annual growth rate of 38% pre-therapeutically, volume stabilization or reduction of all schwannomas along with improvement of pain and neurological deficits, including hearing impairment, were observed under 24 months of bevacizumab. In summary, this is the first report of a sustained response to bevacizumab in a patient shown to carry the frequent mosaic NF2:c.784C>T p.(Arg262*) variant. Our results may be of particular relevance to guide treatment decisions in mosaic NF2 patients harboring this variant.