Single-cell transcriptomic atlas reveals increased regeneration in diseased human inner ear balance organs.

Mammalian inner ear hair cell loss leads to permanent hearing and balance dysfunction. In contrast to the cochlea, vestibular hair cells of the murine utricle have some regenerative capacity. Whether human utricular hair cells regenerate in vivo remains unknown. Here we procured live, mature utricles from organ donors and vestibular schwannoma patients, and present a validated single-cell transcriptomic atlas at unprecedented resolution. We describe markers of 13 sensory and non-sensory cell types, with partial overlap and correlation between transcriptomes of human and mouse hair cells and supporting cells. We further uncover transcriptomes unique to hair cell precursors, which are unexpectedly 14-fold more abundant in vestibular schwannoma utricles, demonstrating the existence of ongoing regeneration in humans. Lastly, supporting cell-to-hair cell trajectory analysis revealed 5 distinct patterns of dynamic gene expression and associated pathways, including Wnt and IGF-1 signaling. Our dataset constitutes a foundational resource, accessible via a web-based interface, serving to advance knowledge of the normal and diseased human inner ear.

Four distinct ipsilateral vestibular schwannomas: A case of mosaic NF2-related schwannomatosis.

OBJECTIVES: Distinguishing between sporadic and germline/mosaic NF2-related schwannomatosis is important to ensure that patients have appropriate long-term care. With this report, we describe a unique case of a patient with 4 ipsilateral schwannomas and identify a combination of sequencing modalities that can accurately diagnose mosaic NF2-related schwannomatosis. METHODS: We present a 32-year-old woman with a familial history of vestibular schwannoma in her father and right-sided schwannomas involving the apical and basal turns of cochlea, lateral semicircular canal, and internal auditory canal (IAC). Genetic analysis of blood and frozen tissue from 2 tumors (intralabyrinthine and IAC tumors) was performed using next-generation sequencing (NGS), multiplex ligation-dependent probe amplification (MLPA), and optical genome mapping (OGM). RESULTS: Germline testing for NF2, LZTR1, and SMARCB1 was negative. Tumor genetic testing revealed a shared NF2 pathogenic variant between the 2 tumors ("first hit") but distinct "second hit" NF2 variants, including mosaic loss of chromosome 22 in the IAC tumor seen only with OGM, consistent with mosaic NF2-related schwannomatosis. CONCLUSIONS: Multimodality sequencing, including NGS, MLPA, and OGM, was required to ensure appropriate diagnosis of mosaic NF2-related schwannomatosis in this patient. A similar approach can be used for other patients with multiple ipsilateral tumors and suspected tumor predisposition.

Unilateral Multifocal Inner Ear and Internal Auditory Canal or Cerebellopontine Angle Cochleovestibular Schwannomas-Genetic Analysis and Management by Surgical Resection and Cochlear Implantation.

OBJECTIVE: To describe the genetic characteristics and the management of two very rare cases of unilateral multifocal inner ear and internal auditory canal or cerebellopontine angle cochleovestibular schwannomas not being associated to full neurofibromatosis type 2-related schwannomatosis. PATIENTS: In a 29-year-old man and a 55-year-old woman with single-sided deafness multifocal unilateral cochleovestibular schwannomas were surgically resected, and hearing was rehabilitated with a cochlear implant (CI). Unaffected tissue was analyzed using next generation sequencing of the NF2 gene. Tumor tissue was analyzed using a 340-parallel sequencing gene panel. MAIN OUTCOME MEASURES: Mutations in the NF2 gene, word recognition score for monosyllables at 65 dB SPL (WRS 65 ) with CI. RESULTS: No disease-causing mutation was detected in the examined sequences in blood leucokytes. All tumor samples revealed, among others, somatic pathogenic NF2 mutations. While the anatomically separate tumors in case 1 were likely molecular identical, the tumors in case 2 showed different genetic patterns. WRS 65 was 55% at 6 years of follow-up and 60% at 4.5 years of follow-up, respectively. CONCLUSIONS: The occurrence of multifocal unilateral cochleovestibular schwannomas without pathogenic variants in NF2 in non-affected blood leucocytes can be associated with mosaic NF2 -related schwannomatosis (case 1), or with likely sporadic mutations (case 2) and may be overlooked due to their extreme rarity. Although challenging, successful hearing rehabilitation could be achieved through surgical resection of the tumors and cochlear implantation.

Single-cell RNA sequencing analysis of vestibular schwannoma reveals functionally distinct macrophage subsets.

BACKGROUND: Vestibular schwannomas (VSs) remain a challenge due to their anatomical location and propensity to growth. Macrophages are present in VS but their roles in VS pathogenesis remains unknown. OBJECTIVES: The objective was to assess phenotypic and functional profile of macrophages in VS with single-cell RNA sequencing (scRNAseq). METHODS: scRNAseq was carried out in three VS samples to examine characteristics of macrophages in the tumour. RT-qPCR was carried out on 10 VS samples for CD14, CD68 and CD163 and a panel of macrophage-associated molecules. RESULTS: scRNAseq revealed macrophages to be a major constituent of VS microenvironment with three distinct subclusters based on gene expression. The subclusters were also defined by expression of CD163, CD68 and IL-1ß. AREG and PLAUR were expressed in the CD68+CD163+IL-1ß+ subcluster, PLCG2 and NCKAP5 were expressed in CD68+CD163+IL-1ß- subcluster and AUTS2 and SPP1 were expressed in the CD68+CD163-IL-1ß+ subcluster. RT-qPCR showed expression of several macrophage markers in VS of which CD14, ALOX15, Interleukin-1ß, INHBA and Colony Stimulating Factor-1R were found to have a high correlation with tumour volume. CONCLUSIONS: Macrophages form an important component of VS stroma. scRNAseq reveals three distinct subsets of macrophages in the VS tissue which may have differing roles in the pathogenesis of VS.

Small RNA Deep Sequencing Uncovers microRNAs Associated with Hearing Loss in Vestibular Schwannoma.

OBJECTIVE: To analyze the correlation between the miRNA expression profile in vestibular schwannoma (VS) tumor tissue and preoperative patient's hearing status, using the RNA-seq technique. METHODS: Nineteen tumor samples were collected from patients operated for VS in a Tertiary Academic Center. Samples were classified into "good hearing" and "poor hearing" study group based on the results of audiometric studies. Tumor miRNA expression was analyzed using high-throughput RNA sequencing (RNA-seq) technique, using NovaSeq 6000 Illumina system. Functional analysis was performed with the use of DIANA miRpath v. 4.0 online tool. RESULTS: The most overexpressed miRNAs in VS samples derived from poor hearing patients belonged to miR 449a/b, miR 15/16-1, and hypoxamiR families. Functional analysis showed that the differentially expressed miRNAs regulate cellular pathways associated with hypoxia, adherence junction functions, and signaling pathways such as Hippo, FOXO, MAPK, and Wnt signaling pathway. CONCLUSION: Our study identified a specific miRNA expression profile in VS tumor tissues that correlates with hearing impairment. These results suggest potential new molecular mechanisms related to hearing loss in the course of VS. LEVEL OF EVIDENCE: 3 (cohort study) Laryngoscope, 134:3778-3785, 2024.

High-throughput RNA sequencing identifies the miRNA expression profile, target genes, and molecular pathways contributing to growth of sporadic vestibular schwannomas.

PURPOSE: To assess the differences in the miRNA expression profile between small (stage I Koos classification) and large solid vestibular schwannoma (VS) tumors, using the RNA-seq technique. METHODS: Twenty tumor samples (10 small and 10 large tumors) were collected from patients operated for VS in a Tertiary Academic Center. Tumor miRNA expression was analyzed using high-throughput RNA sequencing (RNA-seq) technique, with NovaSeq 6000 Illumina system. Bioinformatics analysis was done using statistical software R. Gene enrichment and functional analysis was performed using miRTargetLink 2.0 and DIANA miRpath 3.0 online tools. RESULTS: We identified 9 differentially expressed miRNAs in large VS samples: miR-7, miR-142 (-3p and -5p), miR-155, miR-342, miR-1269, miR-4664, and miR-6503 were upregulated, whereas miR-204 was significantly down-regulated in comparison to small VS samples. Gene enrichment analysis showed that the most enriched target genes were SCD, TMEM43, LMNB2, JARID2, and CCND1. The most enriched functional pathways were associated with lipid metabolism, along with signaling pathways such as Hippo and FOXO signaling pathway. CONCLUSION: We identified a set of 9 miRNAs that are significantly deregulated in large VS in comparison to small, intracanalicular tumors. The functional enrichment analysis of these miRNAs suggests novel mechanisms, such as that lipid metabolism, as well as Hippo and FOxO signaling pathways that may play an important role in VS growth regulation.

Single-cell multi-omic analysis of the vestibular schwannoma ecosystem uncovers a nerve injury-like state.

Vestibular schwannomas (VS) are benign tumors that lead to significant neurologic and otologic morbidity. How VS heterogeneity and the tumor microenvironment (TME) contribute to VS pathogenesis remains poorly understood. In this study, we perform scRNA-seq on 15 VS, with paired scATAC-seq (n = 6) and exome sequencing (n = 12). We identify diverse Schwann cell (SC), stromal, and immune populations in the VS TME and find that repair-like and MHC-II antigen-presenting SCs are associated with myeloid cell infiltrate, implicating a nerve injury-like process. Deconvolution analysis of RNA-expression data from 175 tumors reveals Injury-like tumors are associated with larger tumor size, and scATAC-seq identifies transcription factors associated with nerve repair SCs from Injury-like tumors. Ligand-receptor analysis and in vitro experiments suggest that Injury-like VS-SCs recruit myeloid cells via CSF1 signaling. Our study indicates that Injury-like SCs may cause tumor growth via myeloid cell recruitment and identifies molecular pathways that may be therapeutically targeted.

Identification of hub genes and drug candidates for NF2-related vestibular schwannoma by bioinformatics tools.

Neurofibromatosis type 2 (NF2)-related vestibular schwannoma (NF2-VS) is a rare genetic disorder that results in bilateral acoustic neuromas. However, the exact pathogenesis of the disease is still unclear. This study aims to use bioinformatics analyses to identify potential hub genes and therapeutic. We retrieved the mRNA expression profiles (GSE108524 and GSE141801) of NF2-VS from the database, and selected the leading 25% genes with the most variance across samples for weighted correlation network analysis. Subsequently, we conducted gene ontology term and Kyoto Encyclopedia of Genes and Genomes signaling network enrichment analyses. The STRING database was employed for protein-protein interaction (PPI) axis construction. The mRNA-miRNA modulatory network was generated via the miRTarBase database. Differentially expressed genes (DEGs) were identified via the R package "limma" in both datasets, and hub genes were screened via intersection of common DEGs, candidate hub genes from the PPI axis, and candidate hub genes from the key module. Finally, common DEGs were uploaded onto the connectivity map database to determine drug candidates. Based on our observations, the blue module exhibited the most significant relation to NF2-VS, and it included the NF2 gene. Using enrichment analysis, we demonstrated that the blue modules were intricately linked to modulations of cell proliferation, migration, adhesion, junction, and actin skeleton. Overall, 356 common DEGs were screened in both datasets, and 33 genes carrying a degree > 15 were chosen as candidate hub genes in the PPI axis. Subsequently, 4 genes, namely, GLUL, CAV1, MYH11, and CCND1 were recognized as real hub genes. In addition, 10 drugs with enrichment scores < -0.7 were identified as drug candidates. Our conclusions offered a novel insight into the potential underlying mechanisms behind NF2-VS. These findings may facilitate the identification of novel therapeutic targets in the future.

A Bilateral Vestibular Schwannoma is Not Always Related to Neurofibromatosis Type 2.

Bilateral vestibular schwannomas are commonly diagnosed in patients affected by neurofibromatosis type 2, a genetic disease caused by a heterozygous mutation in the gene region encoding neurofibromin-2. Sporadic bilateral vestibular schwannomas are very rare entities affecting almost exclusively elderly people. We present the case of a senior woman who was followed up with the "wait-and-scan" strategy for a unilateral vestibular schwannoma that later developed as a contralateral tumor, compatible with vestibular schwannoma, raising questions about its nature and risk of having been transmitted in offspring. Genetic testing excluded mutations of the neurofibromatosis type 2 gene. The presence of bilateral vestibular schwannomas is often considered pathognomonic of neurofibromatosis type 2, but the estimated probability of sporadic bilateral tumors in the absence of other neurofibromatosis type 2 features is 50% over 70 years of age. Therefore, the NF2 gene assessment is in any case recommended in these patients not only for an evaluation of the risk of being transmitted. The treatment strategy should be carefully personalized for each patient, considering the size of the tumors, symptoms, and hearing function together with the patient's age.

Identification of key genes and immune infiltration based on weighted gene co-expression network analysis in vestibular schwannoma.

Vestibular schwannomas are the most common tumors of the cerebellopontine angle, but their pathogenesis is still unclear. This study aimed to explore the molecular mechanisms and potential therapeutic target biomarkers in vestibular schwannoma. Two datasets (GSE141801 and GSE54934) were downloaded from the Gene Expression Omnibus database. Weighted gene coexpression network analysis was performed to find the key modules associated with vestibular schwannoma (VS). Functional enrichment analysis was applied to evaluate the gene enrichment signaling pathway in key modules. Protein-protein interaction networks in key modules were constructed using the STRING website. Hub genes were identified by intersecting candidate hub genes in protein-protein interaction network and candidate hub genes in key modules. Single-sample gene set enrichment analysis was utilized to quantify the abundance of tumor-infiltrating immune cells in VSs and normal control nerves. A Random forest classifier was developed based on hub genes identified in this study and validated on an independent dataset (GSE108524). Results of immune cell infiltration were also validated on GSE108524 by gene set enrichment analysis. Eight genes from coexpression modules were identified as hub genes, that is, CCND1, CAV1, GLI1, SOX9, LY86, TLR3, TREM2, and C3AR1, which might be potential therapeutic targets for VS. We also found that there were distinct differences in the infiltration levels of immune cells between VSs and normal control nerves. Overall, our findings may be useful for investigating the mechanisms underlying VS and provide noteworthy directions for future research.

Targeted Therapies in the Treatment of Vestibular Schwannomas: Current State and New Horizons.

Vestibular schwannomas continue to cause hearing loss, facial nerve paralysis, imbalance, and tinnitus. These symptoms are compounded by germline neurofibromatosis type 2 (NF2) gene loss and multiple intracranial and spinal cord tumors associated with NF2-related schwannomatosis. The current treatments of observation, microsurgical resection, or stereotactic radiation may prevent catastrophic brainstem compression but are all associated with the loss of cranial nerve function, particularly hearing loss. Novel targeted treatment options to stop tumor progression include small molecule inhibitors, immunotherapy, anti-inflammatory drugs, radio-sensitizing and sclerosing agents, and gene therapy.

Updates on Tumor Biology in Vestibular Schwannoma.

Vestibular schwannomas (VSs) are benign tumors that develop after biallelic inactivation of the neurofibromatosis type 2 (NF2) gene that encodes the tumor suppressor merlin. Merlin inactivation leads to cell proliferation by dysregulation of receptor tyrosine kinase signaling and other intracellular pathways. In VS without NF2 mutations, dysregulation of non-NF2 genes can promote pathways favoring cell proliferation and tumorigenesis. The tumor microenvironment of VS consists of multiple cell types that influence VS tumor biology through complex intercellular networking and communications.

Tumor Microenvironment in Sporadic Vestibular Schwannoma: A Systematic, Narrative Review.

Although diagnosis and treatment of vestibular schwannomas (VSs) improved in recent years, no factors have yet been identified as being capable of predicting tumor growth. Molecular rearrangements occur in neoplasms before any macroscopic morphological changes become visible, and the former are the underlying cause of disease behavior. Tumor microenvironment (TME) encompasses cellular and non-cellular elements interacting together, resulting in a complex and dynamic key of tumorigenesis, drug response, and treatment outcome. The aim of this systematic, narrative review was to assess the level of knowledge on TME implicated in the biology, behavior, and prognosis of sporadic VSs. A search (updated to November 2022) was run in Scopus, PubMed, and Web of Science electronic databases according to the PRISMA guidelines, retrieving 624 titles. After full-text evaluation and application of inclusion/exclusion criteria, 37 articles were included. VS microenvironment is determined by the interplay of a dynamic ecosystem of stromal and immune cells which produce and remodel extracellular matrix, vascular networks, and promote tumor growth. However, evidence is still conflicting. Further studies will enhance our understanding of VS biology by investigating TME-related biomarkers able to predict tumor growth and recognize immunological and molecular factors that could be potential therapeutic targets for medical treatment.

Advances in Targeted Therapy for Neurofibromatosis Type 2 (NF2)-Associated Vestibular Schwannomas.

PURPOSE OF REVIEW: Neurofibromatosis 2 (NF2) is an autosomal-dominant genetic disorder characterized by bilateral vestibular schwannomas (VS), meningiomas, ependymomas, spinal and peripheral schwannomas, optic gliomas, and juvenile cataracts. Ongoing studies provide new insight into the role of the NF2 gene and merlin in VS tumorigenesis. RECENT FINDINGS: As NF2 tumor biology becomes increasingly understood, therapeutics targeting specific molecular pathways have been developed and evaluated in preclinical and clinical studies. NF2-associated VS are a source of significant morbidity with current treatments including surgery, radiation, and observation. Currently, there are no FDA-approved medical therapies for VS, and the development of selective therapeutics is a high priority. This manuscript reviews NF2 tumor biology and current therapeutics undergoing investigation for treatment of patients with VS.

Herpesviruses, polyomaviruses, parvoviruses, papillomaviruses, and anelloviruses in vestibular schwannoma.

Etiology of vestibular schwannoma (VS) is unknown. Viruses can infect and reside in neural tissues for decades, and new viruses with unknown tumorigenic potential have been discovered. The presence of herpesvirus, polyomavirus, parvovirus, and anellovirus DNA was analyzed by quantitative PCR in 46 formalin-fixed paraffin-embedded VS samples. Five samples were analyzed by targeted next-generation sequencing. Viral DNA was detected altogether in 24/46 (52%) tumor samples, mostly representing anelloviruses (46%). Our findings show frequent persistence of anelloviruses, considered normal virome, in VS. None of the other viruses showed an extensive presence, thereby suggesting insignificant role in VS.

Multiplatform molecular analysis of vestibular schwannoma reveals two robust subgroups with distinct microenvironment.

BACKGROUND: Vestibular schwannoma (VS) is the most common tumour of the cerebellopontine angle and poses a significant morbidity for patients. While many exhibit benign behaviour, others have a more aggressive nature and pattern of growth. Predicting who will fall into which category consistently remains uncertain. There is a need for a better understanding of the molecular landscape, and important subgroups therein, of this disease. METHODS: We select all vestibular schwannomas from our tumour bank with both methylation and RNA profiling available. Unsupervised clustering methods were used to define two distinct molecular subgroups of VS which were explored using computational techniques including bulk deconvolution analysis, gene pathway enrichment analysis, and drug repurposing analysis. Methylation data from two other cohorts were used to validate our findings, given a paucity of external samples with available multi-omic data. RESULTS: A total of 75 tumours were analyzed. Consensus clustering and similarity network fusion defined two subgroups ("immunogenic" and "proliferative") with significant differences in immune, stroma, and tumour cell abundance (p < 0.05). Gene network analysis and computational drug repurposing found critical differences in targets of immune checkpoint inhibition PD-1 and CTLA-4, the MEK pathway, and the epithelial to mesenchymal transition program, suggesting a need for subgroup-specific targeted treatment/trial design in the future. CONCLUSIONS: We leverage computational tools with multi-omic molecular data to define two robust subgroups of vestibular schwannoma with differences in microenvironment and therapeutic vulnerabilities.

Genome-wide association analysis identifies a susceptibility locus for sporadic vestibular schwannoma at 9p21.

Vestibular schwannomas are benign nerve sheath tumours that arise on the vestibulocochlear nerves. Vestibular schwannomas are known to occur in the context of tumour predisposition syndromes NF2-related and LZTR1-related schwannomatosis. However, the majority of vestibular schwannomas present sporadically without identification of germline pathogenic variants. To identify novel genetic associations with risk of vestibular schwannoma development, we conducted a genome-wide association study in a cohort of 911 sporadic vestibular schwannoma cases collated from the neurofibromatosis type 2 genetic testing service in the north-west of England, UK and 5500 control samples from the UK Biobank resource. One risk locus reached genome-wide significance in our association analysis (9p21.3, rs1556516, P = 1.47 × 10-13, odds ratio = 0.67, allele frequency = 0.52). 9p21.3 is a genome-wide association study association hotspot, and a number of genes are localized to this region, notably CDKN2B-AS1 and CDKN2A/B, also referred to as the INK4 locus. Dysregulation of gene products within the INK4 locus have been associated with multiple pathologies and the genes in this region have been observed to directly impact the expression of one another. Recurrent associations of the INK4 locus with components of well-described oncogenic pathways provides compelling evidence that the 9p21.3 region is truly associated with risk of vestibular schwannoma tumorigenesis.

Distinct immune signature predicts progression of vestibular schwannoma and unveils a possible viral etiology.

BACKGROUND: The management of sub-totally resected sporadic vestibular schwannoma (VS) may include observation, re-resection or irradiation. Identifying the optimal choice can be difficult due to the disease's variable progression rate. We aimed to define an immune signature and associated transcriptomic fingerprint characteristic of rapidly-progressing VS to elucidate the underpinnings of rapidly progressing VS and identify a prognostic model for determining rate of progression. METHODS: We used multiplex immunofluorescence to characterize the immune microenvironment in 17 patients with sporadic VS treated with subtotal surgical resection alone. Transcriptomic analysis revealed differentially-expressed genes and dysregulated pathways when comparing rapidly-progressing VS to slowly or non-progressing VS. RESULTS: Rapidly progressing VS was distinctly enriched in CD4+, CD8+, CD20+, and CD68+ immune cells. RNA data indicated the upregulation of anti-viral innate immune response and T-cell senescence. K - Top Scoring Pair analysis identified 6 pairs of immunosenescence-related genes (CD38-KDR, CD22-STAT5A, APCS-CXCR6, MADCAM1-MPL, IL6-NFATC3, and CXCL2-TLR6) that had high sensitivity (100%) and specificity (78%) for identifying rapid VS progression. CONCLUSION: Rapid progression of residual vestibular schwannoma following subtotal surgical resection has an underlying immune etiology that may be virally originating; and despite an abundant adaptive immune response, T-cell immunosenescence may be associated with rapid progression of VS. These findings provide a rationale for clinical trials evaluating immunotherapy in patients with rapidly progressing VS.

Is There an Inherited Contribution to Risk for Sporadic Unilateral Vestibular Schwannoma? Evidence of Familial Clustering.

OBJECT: Unlike the autosomal dominant inheritance of neurofibromatosis 2, there are no known inherited risk factors for sporadic, unilateral vestibular schwannoma (VS), which comprise most VS cases. The authors tested a hypothesis positing a genetic contribution to predisposition to these lesions by analyzing familial clustering of cases. METHODS: Familial clustering of individuals with unilateral VS was analyzed in two independent genealogical resources with linked diagnosis data: the Veterans Health Administration Genealogy Resource and the Utah Population Database. Tests for excess relatedness, estimation of relative risks (RRs) in close and distant relatives, and identification of pedigrees with a significant excess of unilateral VS among descendants were performed. RESULTS: The average pairwise relatedness of the Veterans Health Administration Genealogy Resource VS cases significantly exceeded the expected relatedness ( p = 0.016), even when close relationships were ignored ( p = 0.002). RR for third- and fifth-degree relatives developing VS were significantly elevated (RR, 60.83; p = 0.0005; 95% confidence interval [CI], 7.37-219.73) and (RR, 11.88; p = 0.013; 95% CI, 1.44-42.90), respectively. No VS-affected first-, second-, or fourth-degree relatives were observed. In the Utah Population Database population, no first- or second-degree relatives with VS were observed. RR for fifth-degree relatives developing VS was significantly elevated (RR, 2.23; p = 0.009; 95% CI, 1.15-3.90). CONCLUSION: These results provide strong evidence for an inherited predisposition to sporadic, unilateral VS. This study exhibits the value of genealogical resources with linked medical data for examining hypotheses regarding inherited predisposition. The high-risk unilateral VS pedigrees identified in two independent resources provide a powerful means of pursuing predisposition gene identification.

A mechanistic mathematical model of initiation and malignant transformation in sporadic vestibular schwannoma.

BACKGROUND: A vestibular schwannoma (VS) is a relatively rare, benign tumour of the eighth cranial nerve, often involving alterations to the gene NF2. Previous mathematical models of schwannoma incidence have not attempted to account for alterations in specific genes, and could not distinguish between nonsense mutations and loss of heterozygosity (LOH). METHODS: Here, we present a mechanistic approach to modelling initiation and malignant transformation in schwannoma. Each parameter is associated with a specific gene or mechanism operative in Schwann cells, and can be determined by combining incidence data with empirical frequencies of pathogenic variants and LOH. RESULTS: This results in new estimates for the base-pair mutation rate u = 4.48 × 10-10 and the rate of LOH = 2.03 × 10-6/yr in Schwann cells. In addition to new parameter estimates, we extend the approach to estimate the risk of both spontaneous and radiation-induced malignant transformation. DISCUSSION: We conclude that radiotherapy is likely to have a negligible excess risk of malignancy for sporadic VS, with a possible exception of rapidly growing tumours.