Abstract
Hearing-preserving partial resection of neurofibromatosis type 2 (NF2) associated vestibular schwannomas (VS) is a preferred treatment strategy, particularly for children and adolescents. However, the residual tumors do grow and lead at some point to continued hearing deterioration. An adjuvant bevacizumab treatment may provide an option for slowing down this process. In this retrospective study, we reviewed tumor volume and hearing data of 16 operated VS in nine patients younger than 30 years over a period of 63 to 142 months. All these patients had one or more bevacizumab treatment periods and most of them had a non-treatment period after surgery. Four different patterns of growth were observed for the residual tumors: (1) growth in the non-treatment periods, which slowed down in the treatment periods; (2) growth slowed down in one but not in another on-period; (3) unaffected growth; (4) no or minimal growth regardless of the treatment. Neither radiological regression of tumor volume nor hearing improvement were observed in the treatment periods. Accelerated hearing deterioration was observed in several non-treatment periods, but also in some treatment periods. No straightforward correlation can be drawn between tumor growth and hearing scores. Tumor growth and worsening of hearing between two measurement points were slightly less in the treatment periods; however, the differences were not significant, because variations were large. In conclusion, our comprehensive follow-up on 16 VS in nine NF2 patients did show heterogenous effects of bevacizumab on small residual vestibular schwannomas after surgery both regarding tumor size and hearing preservation. Thus, smaller and slower growing tumor residuals seem to behave differently to bevacizumab than reported for not-operated faster growing VS.
Highlights
Neurofibromatosis type 2 (NF2) is an autosomal-dominant tumor predisposition disorder caused by the inactivation of the neurofibromatosis type 2 (NF2) tumor suppressor gene located on chromosome 22q12 and the functional loss of its protein product merlin [1]
Since bevacizumab treatment was started at a delayed time point, the overall hearing impairment was more advanced at the time of treatment start
Our study only included rather small residual tumors after partial resection with a postoperatively reduced growth rate, as we have shown in a preliminary study (Gugel et al [6])
Summary
Neurofibromatosis type 2 (NF2) is an autosomal-dominant tumor predisposition disorder caused by the inactivation of the NF2 tumor suppressor gene located on chromosome 22q12 and the functional loss of its protein product merlin (moesin-ezrin-radixin-like protein) [1]. The typical hallmark of the disease and key diagnostic criteria are bilateral vestibular schwannomas (VS) and the occurrence of multiple nervous system lesions, including meningiomas, schwannomas and ependymomas. VS-associated comorbidities such as progressive hearing loss, gait disturbances, dizziness and facial palsy are often predominant in childhood and adolescence [2,3]. Genotype–phenotype correlations are known, but the course of the disease is difficult to estimate [4,5]. Radical microsurgery with total tumor removal carries a high risk of hearing loss and facial palsy. Partial resection aiming at the decompression of the internal auditory canals in young NF2 patients provides a more conservative option with improved growth control and hearing stabilization [6,7]. The risk of continuing growth of the residual tumor and hearing deterioration remains
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