NF2 Genetic Alterations in Sporadic Vestibular Schwannomas: Clinical Implications

An algorithmic approach to the management of peripheral nerve tumours

This article reviews the pathology and management of peripheral nerve tumours, including a framework for investigation and decision-making. Most tumours are benign, including schwannomas and neurofibromas, but malignant peripheral nerve sheath tumours can occur. The risk of malignant change is remote for schwannomas but higher for neurofibromas, particularly in neurofibromatosis type 1. Magnetic resonance imaging is useful for defining the relationship of a swelling with adjacent nerves but is not definitive for tissue diagnosis. Increasing size, pain and neurological deficit suggest malignant change and TruCut needle biopsy is indicated, although there is a risk of sampling error. Excision biopsy preserving nerve function may be carried out for benign tumours to relieve symptoms. Malignant tumours require a multidisciplinary approach. Complete surgical excision with clear margins is the only curative treatment and may be supplemented with radiotherapy and chemotherapy. However, prognosis remains poor, particularly for patients with neurofibromatosis.

Tumors of the nervous system and hearing loss: Beyond vestibular schwannomas

Hearing loss is a common side effect of many tumor treatments. However, hearing loss can also occur as a direct result of certain tumors of the nervous system, the most common of which are the vestibular schwannomas (VS). These tumors arise from Schwann cells of the vestibulocochlear nerve and their main cause is the loss of function of NF2, with 95 % of cases being sporadic and 5 % being part of the rare neurofibromatosis type 2 (NF2)-related Schwannomatosis. Genetic variations in NF2 do not fully explain the clinical heterogeneity of VS, and interactions between Schwann cells and their microenvironment appear to be critical for tumor development. Preclinical in vitro and in vivo models of VS are needed to develop prognostic biomarkers and targeted therapies. In addition to VS, other tumors can affect hearing. Meningiomas and other masses in the cerebellopontine angle can compress the vestibulocochlear nerve due to their anatomic proximity. Gliomas can disrupt several neurological functions, including hearing; in fact, glioblastoma multiforme, the most aggressive subtype, may exhibit early symptoms of auditory alterations. Besides, treatments for high-grade tumors, including chemotherapy or radiotherapy, as well as incomplete resections, can induce long-term auditory dysfunction. Because hearing loss can have an irreversible and dramatic impact on quality of life, it should be considered in the clinical management plan of patients with tumors, and monitored throughout the course of the disease.

Is vestibular schwannoma really a benign tumor? Case report and review

Introduction

Vestibular schwannoma (VS) is a benign tumor that develops from Schwann cells of the eighth cranial pair, mainly in the cerebellopontine angle.

Case Presentation

We report the case of a 30-year-old female patient who developed left otalgia associated with neglected tinnitus, the evolution of which was marked by the development of a static cerebellar syndrome and a behavioral disorder, whose brain MRI revealed a locally advanced process in the cerebellopontine angle at the expense of the vestibulocochlear nerve, in favor of a VS, complicated by involvement of the tonsils, which unfortunately led to the patient's death.

Discussion

VS, formerly known as acoustic neuroma, is an extra-axial intracranial tumor that accounts for over 80% of pontocerebellar angle tumors, and is secondary in the majority of cases to inactivation of the neurofibromatosis type 2 (NF2) tumor suppressor gene, either by mutation of the NF2 gene or loss of chromosome 22q. In the majority of cases, it is unilateral and solitary, but in almost 8% of cases, it is associated with NF2. Cerebral MRI is the examination of choice for the detection, characterization, and diagnosis of VS without the need for biopsy, mainly with T1-weighted sequences before and after gadolinium injection. Treatment is based essentially on surgery or radiosurgery, depending on the size, impact, and expertise of the treatment team.

Conclusion

VS remains an important intracranial tumor entity, which can be life-threatening in cases of advanced local invasion.

Hearing Aid in Vestibular-Schwannoma-Related Hearing Loss: A Review

(1) Background: Several types of hearing aids are available for the rehabilitation of vestibular-schwannoma (VS)-related hearing loss. There is a lack of recently published papers regarding this theme. The aim of the present work is to organize current knowledge. (2) Methods: A review of the literature regarding the topics "vestibular schwannoma", "hearing loss", and "hearing aid" was performed. Nineteen studies were thus considered. (3) Results: Conventional hearing aids, contralateral routing of signal (CROS) aids, bone anchored hearing aids (BAHA), and others are available options for hearing rehabilitation in VS patients. The speech discrimination score (SDS) is considered the best measure to assess candidacy for rehabilitation with hearing aids. The best hearing rehabilitative conditions in VS patients when using conventional hearing aid devices are a mild-moderate hearing loss degree with good word recognition (more than 50% SDS). CROS-Aid and BAHA are reported to be beneficial. CROS-Aid expands on the area of receiving hearing. BAHA aids use direct bone-conduction stimulation. Unfortunately, there are no available studies focused specifically on VS patients that compare CROS and BAHA technologies. (4) Conclusions: Hearing aids, CROS, and BAHA are viable options for rehabilitating hearing impairment in VS, but require an accurate case-by-case audiological evaluation for rehabilitating hearing impairment in VS. Further studies are needed to prove if what is currently known about similar hearing illnesses can be confirmed, particularly in the case of VS.

The comparable tumour microenvironment in sporadic and NF2-related schwannomatosis vestibular schwannoma

Bilateral vestibular schwannoma is the hallmark of NF2-related schwannomatosis, a rare tumour predisposition syndrome associated with a lifetime of surgical interventions, radiotherapy and off-label use of the anti-angiogenic drug bevacizumab. Unilateral vestibular schwannoma develops sporadically in non-NF2-related schwannomatosis patients for which there are no drug treatment options available. Tumour-infiltrating immune cells such as macrophages and T-cells correlate with increased vestibular schwannoma growth, which is suggested to be similar in sporadic and NF2-related schwannomatosis tumours. However, differences between NF2-related schwannomatosis and the more common sporadic disease include NF2-related schwannomatosis patients presenting an increased number of tumours, multiple tumour types and younger age at diagnosis. A comparison of the tumour microenvironment in sporadic and NF2-related schwannomatosis tumours is therefore required to underpin the development of immunotherapeutic targets, identify the possibility of extrapolating ex vivo data from sporadic vestibular schwannoma to NF2-related schwannomatosis and help inform clinical trial design with the feasibility of co-recruiting sporadic and NF2-related schwannomatosis patients. This study drew together bulk transcriptomic data from three published Affymetrix microarray datasets to compare the gene expression profiles of sporadic and NF2-related schwannomatosis vestibular schwannoma and subsequently deconvolved to predict the abundances of distinct tumour immune microenvironment populations. Data were validated using quantitative PCR and Hyperion imaging mass cytometry. Comparative bioinformatic analyses revealed close similarities in NF2-related schwannomatosis and sporadic vestibular schwannoma tumours across the three datasets. Significant inflammatory markers and signalling pathways were closely matched in NF2-related schwannomatosis and sporadic vestibular schwannoma, relating to the proliferation of macrophages, angiogenesis and inflammation. Bulk transcriptomic and imaging mass cytometry data identified macrophages as the most abundant immune population in vestibular schwannoma, comprising one-third of the cell mass in both NF2-related schwannomatosis and sporadic tumours. Importantly, there were no robust significant differences in signalling pathways, gene expression, cell type abundance or imaging mass cytometry staining between NF2-related schwannomatosis and sporadic vestibular schwannoma. These data indicate strong similarities in the tumour immune microenvironment of NF2-related schwannomatosis and sporadic vestibular schwannoma.

Imaging biomarkers associated with extra-axial intracranial tumors: a systematic review

Extra-axial brain tumors are extra-cerebral tumors and are usually benign. The choice of treatment for extra-axial tumors is often dependent on the growth of the tumor, and imaging plays a significant role in monitoring growth and clinical decision-making. This motivates the investigation of imaging biomarkers for these tumors that may be incorporated into clinical workflows to inform treatment decisions. The databases from Pubmed, Web of Science, Embase, and Medline were searched from 1 January 2000 to 7 March 2022, to systematically identify relevant publications in this area. All studies that used an imaging tool and found an association with a growth-related factor, including molecular markers, grade, survival, growth/progression, recurrence, and treatment outcomes, were included in this review. We included 42 studies, comprising 22 studies (50%) of patients with meningioma; 17 studies (38.6%) of patients with pituitary tumors; three studies (6.8%) of patients with vestibular schwannomas; and two studies (4.5%) of patients with solitary fibrous tumors. The included studies were explicitly and narratively analyzed according to tumor type and imaging tool. The risk of bias and concerns regarding applicability were assessed using QUADAS-2. Most studies (41/44) used statistics-based analysis methods, and a small number of studies (3/44) used machine learning. Our review highlights an opportunity for future work to focus on machine learning-based deep feature identification as biomarkers, combining various feature classes such as size, shape, and intensity. Systematic Review Registration: PROSPERO, CRD42022306922.

Tumor Biology and Microenvironment of Vestibular Schwannoma-Relation to Tumor Growth and Hearing Loss

Vestibular schwannoma is the most common benign neoplasm of the cerebellopontine angle. It arises from Schwann cells of the vestibular nerve. The first symptoms of vestibular schwannoma include hearing loss, tinnitus, and vestibular symptoms. In the event of further growth, cerebellar and brainstem symptoms, along with palsy of the adjacent cranial nerves, may be present. Although hearing impairment is present in 95% of patients diagnosed with vestibular schwannoma, most tumors do not progress in size or have low growth rates. However, the clinical picture has unpredictable dynamics, and there are currently no reliable predictors of the tumor's behavior. The etiology of the hearing loss in patients with vestibular schwannoma is unclear. Given the presence of hearing loss in patients with non-growing tumors, a purely mechanistic approach is insufficient. A possible explanation for this may be that the function of the auditory system may be affected by the paracrine activity of the tumor. Moreover, initiation of the development and growth progression of vestibular schwannomas is not yet clearly understood. Biallelic loss of the NF2 gene does not explain the occurrence in all patients; therefore, detection of gene expression abnormalities in cases of progressive growth is required. As in other areas of cancer research, the tumor microenvironment is coming to the forefront, also in vestibular schwannomas. In the paradigm of the tumor microenvironment, the stroma of the tumor actively influences the tumor's behavior. However, research in the area of vestibular schwannomas is at an early stage. Thus, knowledge of the molecular mechanisms of tumorigenesis and interactions between cells present within the tumor is crucial for the diagnosis, prediction of tumor behavior, and targeted therapeutic interventions. In this review, we provide an overview of the current knowledge in the field of molecular biology and tumor microenvironment of vestibular schwannomas, as well as their relationship to tumor growth and hearing loss.

Understanding the Molecular Mechanism of Vestibular Schwannoma for Hearing Preservation Surgery: Otologists’ Perspective from Bedside to Bench

Vestibular schwannoma is a clinically benign schwannoma that arises from the vestibulocochlear nerve that causes sensorineural hearing loss. This tumor is clinically and oncologically regarded as a benign tumor as it does not metastasize or invade surrounding tissues. Despite being a benign tumor, its management is difficult and controversial due to the potential serious complications, such as irreversible sensorineural hearing loss, of current interventions. Therefore, preventing hearing loss due to the natural course of the disease and complications of surgery is a challenging issue for an otologist. Improvements have been reported recently in the treatment of vestibular schwannomas. These include advances in intraoperative monitoring systems for vestibular schwannoma surgery where the risk of hearing loss as a complication is decreased. Precise genomic analysis of the tumor would be helpful in determining the characteristics of the tumor for each patient, leading to a better hearing prognosis. These procedures are expected to help improve the treatment of vestibular schwannomas. This review summarizes recent advances in vestibular schwannoma management and treatment, especially in hearing preservation. In addition, recent advances in the understanding of the molecular mechanisms underlying vestibular schwannomas and how these advances can be applied in clinical practice are outlined and discussed, respectively. Moreover, the future directions from the bedside to the bench side are presented from the perspective of otologists.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumours: Tumours of the Ear

In the recently published 5th Edition of the World Health Organisation Classification of Head and Neck Tumours, there are relatively few changes to report in terms of nomenclature in lesions of ear and temporal bone and fewer developments in molecular pathogenesis in comparison to other sites, particularly in sinonasal tract. Ear and temporal bone tumours are rare and biopsy material is limited. As a result, resources in the literature are scarce with few large series, no controlled clinical trials and the approaches to staging and management are not standardised. New entities are difficult to characterise. The number of entries has, however, increased for tumours of the ear and temporal bone (thirteen) compared to the 4th Edition (eleven). Some lesions previously included in the 4th Edition considered to have no site-specific features have been excluded to be discussed elsewhere and other benign lesions that are specific to this site have been included. The tumours and tumour-like entities of ear and temporal bone are discussed here mindful that the chapter in the 5th edition better correlates disease processes with clinical information and imaging and as far as possible standardises nomenclature.

Current Understanding of Hearing Loss in Sporadic Vestibular Schwannomas: A Systematic Review

Objective

Hearing loss is the most common initial symptom in patients with sporadic vestibular schwannomas (SVS). Hearing preservation is an important goal of both conservative and surgical therapy. However, the mechanism of SVS-associated hearing loss remains unclear. Thus, we performed this systematic review to summarize the current understanding of hearing loss in the SVS and distill a testable hypothesis to further illuminate its underlying mechanism.

Methods

A systematic review querying four databases (PubMed, Medline, Embase, and Web of Science) was performed to identify studies evaluating hearing loss in patients with SVS and exploring the potential mechanisms of hearing impairment.

Results

A total of 50 articles were eligible and included in this review. After analysis, the retrieved studies could be categorized into four types: (1) 29 studies explore the relationship between hearing loss and the growth pattern of the tumor (e.g., tumor size/volume, growth rate, tumor location, etc.); (2) ten studies investigate the potential role of cochlear dysfunction in hearing deterioration, including structural abnormality, protein elevation in perilymph, and cochlear malfunctioning; (3) two studies looked into SVS-induced impairment of auditory pathway and cortex; (4) in the rest nine studies, researchers explored the molecular mechanism underlying hearing loss in SVS, which involves molecular and genetic alterations, inflammatory response, growth factors, and other tumor-associated secretions.

Conclusions

Multiple factors may contribute to the hearing impairment in SVS, including the growth pattern of tumor, cochlear dysfunction, impairment of auditory pathway and cortex, genetic and molecular changes. However, our current understanding is still limited, and future studies are needed to explore this multifactorial hypothesis and dig deeper into its underlying mechanism.

Brainstem intraparenchymal schwannoma with genetic analysis: a case report and literature review

Background

Schwannomas are neoplasms that typically arise from the myelin sheath of peripheral nerves and rarely originate within the brain parenchyma. Some case reports present schwannomas arising from the brainstem, but regrowth of the tumor and the efficacy of postoperative irradiation have not been examined. In addition, the genetic background of schwannomas arising from the brainstem has not been investigated.

Case presentation

A 21-year-old male presented with diplopia, dysphagia, and left-sided hemiparesis, dysesthesia, and ataxia. Intracranial imaging showed a heterogeneous mass with a cystic lesion in the pontomedullary junction. Since the tumor caused obstructive hydrocephalus, the patient underwent subtotal tumor resection. A histopathologic evaluation aided a diagnosis of brainstem intraparenchymal schwannoma. Gradual postoperative mass regrowth was recognized. Three-dimensional conformal radiotherapy was performed on the residual mass and surgical cavity. No tumor regrowth was observed 4 years after surgery. To investigate the genetic background of the tumor, target sequences for 36 genes, including NF2, SMARCB1, and LZTR1, and microsatellite analysis for loss of 22q did not show any somatic variants or 22q loss.

Conclusions

We suggest that brainstem schwannomas might differ from conventional schwannomas in their genetic background.

CPI-17 Overexpression and Its Correlation With the NF2 Mutation Spectrum in Sporadic Vestibular Schwannomas

HYPOTHESIS

We hypothesized that CPI-17 expression and NF2 mutations are correlated with merlin phosphorylation in the etiology of sporadic vestibular schwannoma (VS).

BACKGROUND

NF2 gene mutations have been identified in the majority of sporadic and NF2-associated schwannomas and NF2 gene mutations have been shown to result in merlin protein phosphorylation. CPI-17 can drive Ras activity and promote tumorigenic transformation by inhibiting the tumor suppressor merlin. The aim of this study was to determine the correlation between CPI-17 overexpression and the NF2 mutation spectrum in sporadic VS.

METHODS

In this study, we measured CPI-17 expression and identified NF2 gene alterations in a series of sporadic VS samples. Freshly frozen tumor and matched peripheral blood leukocytes from 44 individuals with sporadic VS were analyzed using next-generation sequencing and Sanger sequencing. Western blotting was used to determine the level of merlin phosphorylation, and immunohistochemistry and Western blotting were used to measure CPI-17 expression in the sporadic VS samples. CCK-8 and wound-healing assays were used to determine the influence of CPI-17 overexpression on cell proliferation.

RESULTS

NF2 mutations were identified in 79.5% of sporadic vestibular schwannomas, with all mutations being exclusively somatic. IHC and WB showed the expression of CPI-17 is upregulated in the sporadic VS. NF2 mutation and CPI-17 are positively correlated with merlin phosphorylation. CPI-17 overexpression induces the proliferation of HEI193 cells.

CONCLUSION

NF2 mutations and CPI-17 expression together induce merlin phosphorylation, which is correlated with the tumorigenesis of sporadic VSs.

Therapy of Sporadic and NF2-Related Vestibular Schwannoma

Vestibular schwannoma (VS) is a benign primary brain tumor that occurs sporadic or as part of a genetic syndrome. The most common cause is the mutation of the NF2 tumor suppressor gene that is involved in the production of the protein merlin. Merlin plays a role in cell growth and cell adhesion. In patients with NF2, the VSs arise bilaterally and coincide with other brain tumors. In sporadic VS, the tumor is typically unilateral and does not coincide in combination with other tumors. MRI is the standard imaging technique and can be used to assess the size and aspect of the tumor as well as the progression of disease. The preferred management of large VS in both VS types is surgery with or without adjuvant radiation. The management for the medium- or small-sized VS includes wait and scan, radiotherapy and/or surgery. This choice depends on the preference of the patient and institutional protocols. The outcomes of surgical and radiotherapy treatments are improving due to progress in surgical equipment/approaches, advances in radiation delivery techniques and dose optimizations protocols. The main purpose of the management of VS is preserving function as long as possible in combination with tumor control.

Next Generation Sequencing of Sporadic Vestibular Schwannoma: Necessity of Biallelic NF2 Inactivation and Implications of Accessory Non-NF2 Variants

OBJECTIVES

1) Describe the genetic alterations discovered in a series of sporadic vestibular schwannomas (VS). 2) Identify if more clinically aggressive variants possess different genetic alterations compared to more indolent-behaving VS.

METHODS

Fresh frozen tumor and matched peripheral blood leukocytes from 23 individuals with sporadic VS were analyzed using whole-exome sequencing, tumor whole transcriptome expression profiling (mRNA-Seq), and tumor mate-pair analysis. Source cases included tumors with fast preoperative growth, giant tumors in young patients, tumors with macrocystic change, recurrent tumors following radiation or microsurgery, and indolent small tumors with minimal or no growth before surgery. Somatic and germ-line alterations of the NF2 gene and beyond the NF2 locus were identified and analyzed using complementing analyses.

RESULTS

Biallelic somatic events involving the NF2 gene were discovered in every analyzed tumor specimen with no concurrent NF2 variants identified in matching peripheral blood specimens. Thirteen tumors showed loss of one chromosome 22 (ch22), 4 tumors showed copy-neutral 22q loss of heterozygosity, and 31 unique small variants in the NF2 gene were discovered. Of the latter, 10 were essential splice site, 11 frame shift, 7 stop gain, 2 missense, and 1 in-frame mutation. No other common or recurring NF2 mutations were identified. However, several other notable large chromosomal aberrations were discovered including 2 tumors with loss of a chromosome 21, 3 with loss of an X or Y chromosome, 1 with copy-neutral loss of heterozygosity in chromosome 15, and 1 with loss of 18p and 16q. All of these other major chromosomal abnormalities only occurred in tumors demonstrating a more aggressive phenotype.

CONCLUSIONS

To date, few studies have used whole-exome sequencing, mate-pair analysis, and RNA-seq to profile genome-wide alterations in sporadic VS. Using high-throughput deep sequencing, "two-hit" alterations in the NF2 gene were identified in every tumor and were not present in peripheral blood supporting that all events were somatic. Type of NF2 gene alteration and accessory mutations outside the NF2 locus may predict phenotypic expression and clinical course.

Biomarkers in Vestibular Schwannoma-Associated Hearing Loss

Vestibular schwannomas (VSs) are benign tumors composed of differentiated neoplastic Schwann cells. They can be classified into two groups: sporadic VS and those associated with neurofibromatosis type 2 (NF2). VSs usually grow slowly, initially causing unilateral sensorineural hearing loss (HL) and tinnitus. These tumors cause HL both due to compression of the auditory nerve or the labyrinthine artery and due to the secretion of different substances potentially toxic to the inner ear or the cochlear nerve. As more and more patients are diagnosed and need to be managed, we are more than ever in need of searching for biomarkers associated with these tumors. Owing to an unknown toxic substance generated by the tumor, HL in VS may be linked to a high protein amount of perilymph. Previous studies have identified perilymph proteins correlated with tumor-associated HL, including μ-Crystallin (CRYM), low density lipoprotein receptor-related protein 2 (LRP2), immunoglobulin (Ig) γ-4 chain C region, Ig κ-chain C region, complement C3, and immunoglobulin heavy constant γ 3. Besides, the presence of specific subtypes of heat shock protein 70 has been suggested to be associated with preservation of residual hearing. It has been recently demonstrated that chemokine receptor-4 (CXCR4) is overexpressed in sporadic VS as well as in NF2 tumors and that hearing disability and CXCR4 expression may be correlated. Further, the genetic profile of VS and its relationship with poor hearing has also been studied, including DNA methylation, deregulated genes, growth factors, and NF2 gene mutations. The knowledge of biomarkers associated with VS would be of significant value to maximize outcomes of hearing preservation in these patients.

Age-dependent copy number variations of TP53 tumour suppressor gene associated with altered phosphorylation status of p53 protein in sporadic schwannomas

PURPOSE

Point mutations of TP53 tumour suppressor are very rare in schwannomas. We aim to characterize the frequency of exonic copy-number changes of the gene in the tumour and to examine the association between TP53 alterations, phosphorylation status of p53 protein and clinical phenotypes.

METHODS

The alterations of TP53 were screened by a combination of Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA) in a total of 44 vestibular schwannomas. The mutation index (MI) in a tumour was defined as the number of exons mutated/ the number of exons tested. Phosphorylation status of p53 protein was investigated by immunoblotting and immunofluorescence.

RESULTS

MLPA analysis showed single and multi-exon deletion mutations of TP53 in 65.7% of the cases. Comparisons of clinical features between mutated and non-mutated patients established an association of TP53 mutations with progressive phenotypes, including an earlier formation and a larger tumour. In addition, there were significant correlations between MI and both patients' age and tumour size. The Ser 392 phosphorylation level of p53 varied among tumours, and correlation analysis revealed an age-dependent phosphorylation pattern. The majority of tumours with hyperphosphorylated p53 were from mutated and young patients, suggesting an association of Ser392 phosphorylation with the mutational status of TP53 involved in the acceleration of tumour growth in young individuals. Moreover, Ser 392 phosphorylation contributed to a nuclear accumulation of p53 in schwannona cultures with TP53 mutation.

CONCLUSIONS

An interplay between the mutation status of TP53, phosphorylation patterns and tumour behaviors might be established in the disease.

Proposal for Modification of Cahan's Criteria Utilizing Molecular Genetic Analyses for Cases without Baseline Histopathology: A Unique Method Applicable to Primary Radiosurgery

Background  Cahan's criteria have been utilized since 1948 to establish causality between prior radiation treatment and the development of secondary malignancy. One major criterion specifies that histological and radiographic evidence collected before and after radiation treatment must confirm separate tumor types; however, pretreatment biopsy is rarely obtained prior to radiosurgery for vestibular schwannoma and many other skull base and cranial lesions. Therefore, in these cases Cahan's criteria cannot be validly applied. Objective  This article proposes an update to Cahan's criteria using modern molecular genetic analysis for cases lacking baseline histopathology. Methods  Mate-pair sequencing and whole exome sequencing of a cerebellopontine angle undifferentiated high-grade pleomorphic sarcoma (UHGPS) that developed after stereotactic radiosurgery of a presumed benign vestibular schwannoma. Results  Mate-pair sequencing and whole exome sequencing of the sarcoma revealed complex chromosomal aberrations. Notably, the tumor contained a deletion in the NF2 gene at 22q12 and an in-frame deletion on exon 5 of the remaining copy of NF2 . Biallelic events impacting NF2 are atypical for UHGPS but are characteristic for vestibular schwannoma. These findings help support the conclusion that the UHGPS arose from a benign vestibular schwannoma all along. Conclusions  Next-generation sequencing can be successfully applied to a radiation-induced sarcoma when both the original and malignant tumors harbor separate signature genetic markers. As our understanding of the genetic profile of various tumors expand, we believe that next-generation sequencing and other genomic tools will play an increasingly important role in establishing causality between radiation and the development of secondary malignancy.

Differential NF2 Gene Status in Sporadic Vestibular Schwannomas and its Prognostic Impact on Tumour Growth Patterns

The great majority of sporadic vestibular schwannomas (VSs) are due to the inactivation of the NF2 gene. In this study, we found age-dependent differences in the clinical parameters of sporadic VSs. Young patients were characterized by progressive tumour behaviours, including earlier onset of initial symptoms, shorter symptom duration and larger tumour size. An increased rate of "two-hits" of both NF2 alleles, usually by mutation and allelic loss, was observed in young cases compared to older, and this correlated with the loss of protein and mRNA expression. In contrast, the tumours with a single mutation (referred to as 'one-hit') exhibited obvious expression levels. Moreover, a mixture of merlin-expressing tumour cells and non-expressing tumour cells was observed in 'one-hit' schwannomas, suggesting that a subset of 'one-hit' tumour cells was present in these tumours. To mimic the growth promoting effects by the second hit, we performed lentivirus-mediated NF2 knockdown in the 'one-hit' schwannoma cultures. Following the loss of NF2 expression, schwannoma cultures demonstrated increased proliferation rates. Above all, we have identified a correlation between the NF2 status and the growth patterns of sporadic VSs. The treatment decision-making, microsurgery or "wait and scan" strategy, should be carried out according to the tumour's genetic background.

Differential NF2 Gene Status in Sporadic Vestibular Schwannomas and its Prognostic Impact on Tumour Growth Patterns

The great majority of sporadic vestibular schwannomas (VSs) are due to the inactivation of the NF2 gene. In this study, we found age-dependent differences in the clinical parameters of sporadic VSs. Young patients were characterized by progressive tumour behaviours, including earlier onset of initial symptoms, shorter symptom duration and larger tumour size. An increased rate of “two-hits” of both NF2 alleles, usually by mutation and allelic loss, was observed in young cases compared to older, and this correlated with the loss of protein and mRNA expression. In contrast, the tumours with a single mutation (referred to as ‘one-hit’) exhibited obvious expression levels. Moreover, a mixture of merlin-expressing tumour cells and non-expressing tumour cells was observed in ‘one-hit’ schwannomas, suggesting that a subset of ‘one-hit’ tumour cells was present in these tumours. To mimic the growth promoting effects by the second hit, we performed lentivirus-mediated NF2 knockdown in the ‘one-hit’ schwannoma cultures. Following the loss of NF2 expression, schwannoma cultures demonstrated increased proliferation rates. Above all, we have identified a correlation between the NF2 status and the growth patterns of sporadic VSs. The treatment decision-making, microsurgery or “wait and scan” strategy, should be carried out according to the tumour’s genetic background.

Molecular Analysis of Hybrid Neurofibroma/Schwannoma Identifies Common Monosomy 22 and α-T-Catenin/CTNNA3 as a Novel Candidate Tumor Suppressor

Neurofibromas and schwannomas are benign Schwann cell-derived peripheral nerve sheath tumors arising sporadically and within neurofibromatoses. Multiple tumors are a hallmark of neurofibromatosis type 1 (NF1) and type 2 (NF2) and schwannomatosis. Neurofibromas in NF1 and schwannomas in NF2 or schwannomatosis are defined by distinctive molecular hits. Among these, multiple hybrid neurofibromas/schwannomas may also appear, not yet being defined by a molecular background. We therefore performed molecular analysis of 22 hybrid neurofibromas/schwannomas using array comparative genomic hybridization, immunohistochemistry, quantitative RT-PCR, and functional analyses of cultured Schwann cells. Furthermore, we analyzed SMARCB1 by fluorescence in situ hybridization and multiplex ligation-dependent probe. Monosomy 22 was identified in 44% of tumors of tested patients with hybrid neurofibromas/schwannomas. In addition, in a single case, we detected focal deletion of the α-T-catenin/CTNNA3 gene (10q21.3). To further characterize this candidate, transient knockdown of α-T-catenin in Schwann cells was performed. CTNNA3 depleted cells showed cytoskeletal abnormalities and reduced E-cadherin expression, indicating epithelial-mesenchymal transition-like abnormalities. To conclude, we uncovered loss of chromosome 22 in almost half of all cases with hybrid neurofibromas/schwannomas of patients with multiple peripheral nerve sheath tumors. We tagged α-T-catenin/CTNNA3 as a novel candidate gene. Our functional investigations might indicate involvement of α-T-catenin/CTNNA3 in the biology of peripheral nerve sheath tumors.

A Diagnostic Dilemma: Multiple Primary Intracranial Tumors Without Vestibular Schwannomas

Sinonasal schwannomas with intracranial extension are exceedingly rare, with only 7 cases reported in the literature. Schwannomas can be isolated or multiple and are commonly associated with familial disorders such as neurofibromatosis 2 (NF 2) or familial schwannomatosis or in sporadic cases seen in sporadic schwannomatosis. Nearly all people with NF2 older than 30 years of age will have the hallmark of bilateral vestibular schwannomas (VS). This case highlights a reported case of an adult with separate primary intracranial tumors. We review the diagnostic criteria of NF2 and schwannomatosis, a recently described third variant of neurofibromatosis. In this case, we incorporate family history, histopathology, and the pathophysiology of both disorders to help determine a diagnosis for this patient.

The importance of nerve microenvironment for schwannoma development

Schwannomas are predominantly benign nerve sheath neoplasms caused by Nf2 gene inactivation. Presently, treatment options are mainly limited to surgical tumor resection due to the lack of effective pharmacological drugs. Although the mechanistic understanding of Nf2 gene function has advanced, it has so far been primarily restricted to Schwann cell-intrinsic events. Extracellular cues determining Schwann cell behavior with regard to schwannoma development remain unknown. Here we show pro-tumourigenic microenvironmental effects on Schwann cells where an altered axonal microenvironment in cooperation with injury signals contribute to a persistent regenerative Schwann cell response promoting schwannoma development. Specifically in genetically engineered mice following crush injuries on sciatic nerves, we found macroscopic nerve swellings in mice with homozygous nf2 gene deletion in Schwann cells and in animals with heterozygous nf2 knockout in both Schwann cells and axons. However, patient-mimicking schwannomas could only be provoked in animals with combined heterozygous nf2 knockout in Schwann cells and axons. We identified a severe re-myelination defect and sustained macrophage presence in the tumor tissue as major abnormalities. Strikingly, treatment of tumor-developing mice after nerve crush injury with medium-dose aspirin significantly decreased schwannoma progression in this disease model. Our results suggest a multifactorial concept for schwannoma formation—emphasizing axonal factors and mechanical nerve irritation as predilection site for schwannoma development. Furthermore, we provide evidence supporting the potential efficacy of anti-inflammatory drugs in the treatment of schwannomas.

Tumor Biology of Vestibular Schwannoma: A Review of Experimental Data on the Determinants of Tumor Genesis and Growth Characteristics

OBJECTIVE

Provide an overview of the literature on vestibular schwannoma biology with special attention to tumor behavior and targeted therapy.

BACKGROUND

Vestibular schwannomas are benign tumors originating from the eighth cranial nerve and arise due to inactivation of the NF2 gene and its product merlin. Unraveling the biology of these tumors helps to clarify their growth pattern and is essential in identifying therapeutic targets.

METHODS

PubMed search for English-language articles on vestibular schwannoma biology from 1994 to 2014.

RESULTS

Activation of merlin and its role in cell signaling seem as key aspects of vestibular schwannoma biology. Merlin is regulated by proteins such as CD44, Rac, and myosin phosphatase-targeting subunit 1. The tumor-suppressive functions of merlin are related to receptor tyrosine kinases, such as the platelet-derived growth factor receptor and vascular endothelial growth factor receptor. Merlin mediates the Hippo pathway and acts within the nucleus by binding E3 ubiquiting ligase CRL4. Angiogenesis is an important mechanism responsible for the progression of these tumors and is affected by processes such as hypoxia and inflammation. Inhibiting angiogenesis by targeting vascular endothelial growth factor receptor seems to be the most successful pharmacologic strategy, but additional therapeutic options are emerging.

CONCLUSION

Over the years, the knowledge on vestibular schwannoma biology has significantly increased. Future research should focus on identifying new therapeutic targets by investigating vestibular schwannoma (epi)genetics, merlin function, and tumor behavior. Besides identifying novel targets, testing new combinations of existing treatment strategies can further improve vestibular schwannoma therapy.

Factors influencing the growth rate of vestibular schwannoma in patients with neurofibromatosis type 2

BACKGROUND

Neurofibromatosis type 2 (NF2) is a devastating disease with no well-accepted management guidelines. Better understanding of the disease process provides the basis for how or when to initiate treatment. Only few studies have addressed the factors influencing the growth rate of NF2-related vestibular schwannomas (VSs), and these studies have reported variable results. This study aimed to assess the clinical factors influencing the growth rate of NF2-related VSs.

METHODS

The medical records of 66 patients (totalling 74 VSs) were retrospectively analysed. The tumours were measured according to a two-component box model. The tumour growth rate was estimated by linear regression analysis of the changes in VS volumes over time. The clinical characteristics of all the patients were recorded. The relationship between the tumour growth rate and clinical factors were analysed. Linear regression, Pearson's correlation and Student's t-test were conducted using the SPSS 19.0 statistical package.

RESULTS

The median follow-up duration was 4.9 years. The VSs growth rate was highly correlated with the initial VS volume (r = 0.97, p < 0.01). However, it was inversely correlated with the age at symptom onset (r = -0.41, p < 0.01). The average VS growth rate in patients with spinal tumours was 13.18 cm(3)/year compared with 0.19 cm(3)/year in patients without spinal tumours (p < 0.01). The VS growth rate in patients who had resection of a contralateral VS was slightly higher than that of patients with untreated VSs (p < 0.01). Other factors including sex, vestibular symptom, presence of other cranial schwannomas, family history and dermal abnormalities did not affect the VS growth rate.

CONCLUSIONS

The potential clinical factors influencing the VS growth rate are the age at symptom onset, initial tumour volume and presence of spinal tumours. Surgical resection of VSs might accelerate the growth rate of contralateral tumours. The effects of these factors require further experimental confirmation.

Alterations in the NF2/LATS1/LATS2/YAP Pathway in Schwannomas

Schwannomas are benign nerve sheath tumors composed of well-differentiated Schwann cells. Other than frequent NF2 (neurofibromatosis type 2) mutations (50%-60%), their molecular pathogenesis is not fully understood. LATS1 and LATS2 are downstream molecules of NF2 and are negative regulators of the yes-associated protein (YAP) oncogene in the Hippo signaling pathway. We assessed mutations of the NF2, LATS1, and LATS2 genes, promoter methylation of LATS1 and LATS2, and expression of YAP and phosphorylated YAP in 82 cases of sporadic schwannomas. Targeted sequencing using the Ion Torrent Proton instrument revealed NF2 mutations in 45 cases (55%), LATS1 mutations in 2 cases (2%), and LATS2 mutations in 1 case (1%) of schwannoma. Methylation-specific polymerase chain reaction showed promoter methylation of LATS1 and LATS2 in 14 cases (17%) and 25 cases (30%), respectively. Overall, 62 cases (76%) had at least 1 alteration in the NF2, LATS1, and/or LATS2 genes. Immunohistochemistry revealed nuclear YAP expression in 18 of 42 cases of schwannoma (43%) and reduced cytoplasmic phosphorylated YAP expression in 15 of 49 cases of schwannoma (31%), all of which had at least 1 alteration in the NF2, LATS1, and/or LATS2 genes. These results suggest that an abnormal Hippo signaling pathway is involved in the pathogenesis of most sporadic schwannomas.

Schwannomas exhibit distinct size-dependent gene-expression patterns

AIM

Neurofibromatosis type 2 (NF2)-associated vestibular schwannomas have variable size at presentation which presents a unique challenge in NF2 patient management. Therefore, we investigated the molecular signature characteristic of the differences in size for improved individualized precise therapy.

MATERIALS & METHODS

RNA expression analysis was performed on 15 small and 27 large NF2-associated vestibular schwannoma tumors using a microarray analyzing over 47,000 transcripts.

RESULTS

A signature of 11 genes was found to be correlated with NF2 tumor size.

CONCLUSION

We have identified the genetic hallmark that differentiates large NF2-associated tumors from smaller tumors. This is the first time that these genes have been shown to be the hallmark for NF2 tumor size.

Using the neurofibromatosis tumor predisposition syndromes to understand normal nervous system development

Development is a tightly regulated process that involves stem cell self-renewal, differentiation, cell-to-cell communication, apoptosis, and blood vessel formation. These coordinated processes ensure that tissues maintain a size and architecture that is appropriate for normal tissue function. As such, tumors arise when cells acquire genetic mutations that allow them to escape the normal growth constraints. In this regard, the study of tumor predisposition syndromes affords a unique platform to better understand normal development and the process by which normal cells transform into cancers. Herein, we review the processes governing normal brain development, discuss how brain cancer represents a disruption of these normal processes, and highlight insights into both normal development and cancer made possible by the study of tumor predisposition syndromes.