Glioblastoma remodelling of human neural circuits decreases survival.

Gliomas synaptically integrate into neural circuits1,2. Previous research has demonstrated bidirectional interactions between neurons and glioma cells, with neuronal activity driving glioma growth1-4 and gliomas increasing neuronal excitability2,5-8. Here we sought to determine how glioma-induced neuronal changes influence neural circuits underlying cognition and whether these interactions influence patient survival. Using intracranial brain recordings during lexical retrieval language tasks in awake humans together with site-specific tumour tissue biopsies and cell biology experiments, we find that gliomas remodel functional neural circuitry such that task-relevant neural responses activate tumour-infiltrated cortex well beyond the cortical regions that are normally recruited in the healthy brain. Site-directed biopsies from regions within the tumour that exhibit high functional connectivity between the tumour and the rest of the brain are enriched for a glioblastoma subpopulation that exhibits a distinct synaptogenic and neuronotrophic phenotype. Tumour cells from functionally connected regions secrete the synaptogenic factor thrombospondin-1, which contributes to the differential neuron-glioma interactions observed in functionally connected tumour regions compared with tumour regions with less functional connectivity. Pharmacological inhibition of thrombospondin-1 using the FDA-approved drug gabapentin decreases glioblastoma proliferation. The degree of functional connectivity between glioblastoma and the normal brain negatively affects both patient survival and performance in language tasks. These data demonstrate that high-grade gliomas functionally remodel neural circuits in the human brain, which both promotes tumour progression and impairs cognition.

Clinical and methylomic features of spinal meningiomas.

PURPOSE: The objective of our study was to analyze methylomic and clinical features of a cohort of spinal meningiomas (SMs) resected at our institution. METHODS: This is a retrospective study of patients undergoing SM resection at our institution between 2010 and 2023. Clinical and radiographic characteristics were reviewed and analyzed with standard statistical methods. A Partitioning Around Medoids approach was used to cluster SMs with methylation data in a combined cohort from our institution and a publicly available dataset by methylation profiles. Clinical variables and pathway analyses were compared for the resulting clusters. RESULTS: Sixty-five SMs were resected in 53 patients with median radiographic follow-up of 34 months. Forty-six (87%) patients were female. The median age at surgery was 65 years and median tumor diameter was 1.9 cm. The five-year progression-free survival rate was 90%, with subtotal resection being associated with recurrence or progression (p = .017). SMs clustered into hypermethylation, intermediate methylation, and hypomethylation subgroups. Tumors in the hypermethylated subgroup were associated with higher WHO grade (p = .046) and higher risk histological subtypes (p <.001), while tumors in the hypomethylated subgroup were least likely to present with copy-number loss in chromosome 22q (p <.0001). SMs classified as immune-enriched under a previously developed intracranial meningioma classifier did not have increased leukocyte fractions or hypomethylation of genes typically hypomethylated in immune-enriched tumors. CONCLUSION: SMs are more benign than their intracranial counterparts, and gross-total resection results in long term PFS. Methylation profiling identifies subgroups with differences in clinical variables.

Radiotherapy for meningiomas.

Meningiomas are the most common primary central nervous system neoplasm. Despite promising recent progress in elucidating the genomic landscape and underlying biology of these histologically, molecularly, and clinically diverse tumors, the mainstays of meningioma treatment remain maximal safe resection and radiation therapy. The aim of this review of meningioma radiotherapy is to provide a concise summary of the history, current evidence, and future for application of radiotherapy in meningioma treatment.

Meningeal solitary fibrous tumor cell states phenocopy cerebral vascular development and homeostasis.

BACKGROUND: Meningeal solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that are associated with local recurrence and hematogenous metastasis. The cell states and spatial transcriptomic architecture underlying the unique clinical behavior of meningeal SFTs are unknown. METHODS: Single-cell (n=4), spatial (n=8), and bulk RNA sequencing (n=22) was used to define the cell states and spatial transcriptomic architecture of meningeal SFTs across histological grades and in patient-matched pairs of primary/recurrent or intracranial/metastatic samples. Immunofluorescence, immunohistochemistry, and comparison of single-cell types to meningiomas, or to cerebral vascular development or homeostasis, were used for validation. RESULTS: Here we show meningeal SFTs are comprised of regionally distinct gene expression programs that resemble cerebral vascular development or homeostasis. Single-cell trajectory analysis and pseudotemporal ordering of single-cells suggest that meningeal SFT cell fate decisions are dynamic and interchangeable. Cell-cell communication analyses demonstrate receptor-ligand interactions throughout the meningeal SFT microenvironment, particularly between SFT cells, endothelia, and immature neurons. Direct comparison of single-cell transcriptomes from meningeal SFTs versus meningiomas shows that SFT cells are enriched in expression of endothelial markers while meningiomas cells are enriched in expression of mural cells markers. Meningeal SFT spatial transcriptomes show regionally distinct intratumor heterogeneity in cell states, gene expression programs, and cell-cell interactions across WHO histological grades and in patient-matched pairs of primary/recurrent or intracranial/metastatic samples. CONCLUSIONS: These results shed light on pathways underlying meningeal SFT biology in comparison to other central nervous system tumors and provide a framework for integrating single-cell, spatial, and bulk RNA sequencing data across human cancers and normal tissues.

Calcified Meningiomas Demonstrate Equivocal Grade, Proliferation, and Immediate Surgical Outcomes.

BACKGROUND/OBJECTIVE: Meningioma calcification is thought to predict reduced growth potential and aggression. However, historical studies have primarily focused on correlating calcification in small meningiomas (diameter less than 2.5 cm) rather than analyzing characteristics of calcified meningiomas across all sizes. In this study, we investigate the pathologic and clinical implications of meningioma calcification. METHODS: We utilized a historical database of 342 consecutive newly diagnosed intracranial meningiomas with preoperative computed tomography and magnetic resonance imaging scans treated at a single institution from 2005 to 2019. We correlated the presence of calcification with patient demographics, grade, Mindbomb Homolog-1 index, location, volume, Simpson grade, and recurrence using both univariate and multivariate generalized linear models. RESULTS: On univariate analysis, no single variable correlated with tumor calcification. Notably, neither tumor 2021 World Health Organization grade (P = 0.91) nor Mindbomb Homolog-1 index (P = 0.62) predicted calcification. After accounting for demographic characteristics and tumor volume and location, there was no significant association between 2021 World Health Organization grade (P = 0.52) and Mindbomb Homolog-1 index (P = 0.54) and calcification. Calcification had no influence on resection grade (P = 0.59) or recurrence (P = 0.80). CONCLUSIONS: In this series, calcified meningiomas exhibited similar 2021 World Health Organization tumor grading distribution, proliferation indexes, and immediate surgical outcomes compared to their noncalcified counterparts. These findings question the historical role of using meningioma calcification as an independent guide to their management.

Epidemiology, Genetics, and DNA Methylation Grouping of Hyperostotic Meningiomas.

BACKGROUND AND OBJECTIVES: Meningiomas are the most common primary intracranial tumors and are among the only tumors that can form lamellar, hyperostotic bone in the tumor microenvironment. Little is known about the epidemiology or molecular features of hyperostotic meningiomas. METHODS: Using a retrospective database of 342 meningiomas treated with surgery at a single institution, we correlated clinical, tumor-related, targeted next-generation DNA sequencing (n = 39 total, 16 meningioma-induced hyperostosis [MIH]), and surgical variables with the presence of MIH using generalized linear models. Meningioma DNA methylation grouping was analyzed on a separate population of patients from the same institution with preoperative imaging studies sufficient for identification of MIH (n = 200). RESULTS: MIH was significantly correlated with anterior fossa (44.3% of MIH vs 17.5% of non-MIH were in the anterior fossa P < .001, c2) or skull base location (62.5% vs 38.3%, P < .001, c2) and lower MIB-1 labeling index. Gross total resection was accomplished in 27.3% of tumors with MIH and 45.5% of nonhyperostotic meningiomas (P < .05, t test). There was no association between MIH and histological World Health Organization grade (P = .32, c2). MIH was significantly more frequent in meningiomas from the Merlin-intact DNA methylation group (P < .05). Somatic missense mutations in the WD-repeat-containing domain of the TRAF7 gene were the most common genetic alteration associated with MIH (n = 12 of 15, 80%, P < .01, c2). CONCLUSION: In this article, we show that MIH has a predilection for the anterior skull base and affected tumors are less amenable to gross total resection. We find no association between MIH and histological World Health Organization grade, but show that MIH is more common in the Merlin-intact DNA methylation group and is significantly associated with TRAF7 somatic missense mutations. These data provide a framework for future investigation of biological mechanisms underlying MIH.

MerlinS13 phosphorylation regulates meningioma Wnt signaling and magnetic resonance imaging features.

Meningiomas are associated with inactivation of NF2/Merlin, but approximately one-third of meningiomas with favorable clinical outcomes retain Merlin expression. Biochemical mechanisms underlying Merlin-intact meningioma growth are incompletely understood, and non-invasive biomarkers that may be used to guide treatment de-escalation or imaging surveillance are lacking. Here, we use single-cell RNA sequencing, proximity-labeling proteomic mass spectrometry, mechanistic and functional approaches, and magnetic resonance imaging (MRI) across meningioma xenografts and patients to define biochemical mechanisms and an imaging biomarker that underlie Merlin-intact meningiomas. We find Merlin serine 13 (S13) dephosphorylation drives meningioma Wnt signaling and tumor growth by attenuating inhibitory interactions with ß-catenin and activating the Wnt pathway. MRI analyses show Merlin-intact meningiomas with S13 phosphorylation and favorable clinical outcomes are associated with high apparent diffusion coefficient (ADC). These results define mechanisms underlying a potential imaging biomarker that could be used to guide treatment de-escalation or imaging surveillance for patients with Merlin-intact meningiomas.

Spatial genomic, biochemical and cellular mechanisms underlying meningioma heterogeneity and evolution.

Intratumor heterogeneity underlies cancer evolution and treatment resistance, but targetable mechanisms driving intratumor heterogeneity are poorly understood. Meningiomas are the most common primary intracranial tumors and are resistant to all medical therapies, and high-grade meningiomas have significant intratumor heterogeneity. Here we use spatial approaches to identify genomic, biochemical and cellular mechanisms linking intratumor heterogeneity to the molecular, temporal and spatial evolution of high-grade meningiomas. We show that divergent intratumor gene and protein expression programs distinguish high-grade meningiomas that are otherwise grouped together by current classification systems. Analyses of matched pairs of primary and recurrent meningiomas reveal spatial expansion of subclonal copy number variants associated with treatment resistance. Multiplexed sequential immunofluorescence and deconvolution of meningioma spatial transcriptomes using cell types from single-cell RNA sequencing show decreased immune infiltration, decreased MAPK signaling, increased PI3K-AKT signaling and increased cell proliferation, which are associated with meningioma recurrence. To translate these findings to preclinical models, we use CRISPR interference and lineage tracing approaches to identify combination therapies that target intratumor heterogeneity in meningioma cell co-cultures.

Perivascular NOTCH3+ Stem Cells Drive Meningioma Tumorigenesis and Resistance to Radiotherapy.

Meningiomas are the most common primary intracranial tumors. Treatments for patients with meningiomas are limited to surgery and radiotherapy, and systemic therapies remain ineffective or experimental. Resistance to radiotherapy is common in high-grade meningiomas and the cell types and signaling mechanisms that drive meningioma tumorigenesis and resistance to radiotherapy are incompletely understood. Here, we report that NOTCH3 drives meningioma tumorigenesis and resistance to radiotherapy and find that perivascular NOTCH3+ stem cells are conserved across meningiomas from humans, dogs, and mice. Integrating single-cell transcriptomics with lineage tracing and imaging approaches in genetically engineered mouse models and xenografts, we show NOTCH3 drives tumor-initiating capacity, cell proliferation, angiogenesis, and resistance to radiotherapy to increase meningioma growth and reduce survival. To translate these findings to patients, we show that an antibody stabilizing the extracellular negative regulatory region of NOTCH3 blocks meningioma tumorigenesis and sensitizes meningiomas to radiotherapy, reducing tumor growth and improving survival. Significance: There are no effective systemic therapies to treat meningiomas, and meningioma stem cells are poorly understood. Here, we report perivascular NOTCH3+ stem cells to drive meningioma tumorigenesis and resistance to radiotherapy. Our results identify a conserved mechanism and a therapeutic vulnerability to treat meningiomas that are resistant to standard interventions.

Epigenetic reprogramming shapes the cellular landscape of schwannoma.

Mechanisms specifying cancer cell states and response to therapy are incompletely understood. Here we show epigenetic reprogramming shapes the cellular landscape of schwannomas, the most common tumors of the peripheral nervous system. We find schwannomas are comprised of 2 molecular groups that are distinguished by activation of neural crest or nerve injury pathways that specify tumor cell states and the architecture of the tumor immune microenvironment. Moreover, we find radiotherapy is sufficient for interconversion of neural crest schwannomas to immune-enriched schwannomas through epigenetic and metabolic reprogramming. To define mechanisms underlying schwannoma groups, we develop a technique for simultaneous interrogation of chromatin accessibility and gene expression coupled with genetic and therapeutic perturbations in single-nuclei. Our results elucidate a framework for understanding epigenetic drivers of tumor evolution and establish a paradigm of epigenetic and metabolic reprograming of cancer cells that shapes the immune microenvironment in response to radiotherapy.

Meningeal solitary fibrous tumor cell states phenocopy cerebral vascular development and homeostasis.

Meningeal solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that are associated with hematogenous metastasis, and the cell states and spatial transcriptomic architecture of SFTs are unknown. Here we use single-cell and spatial RNA sequencing to show SFTs are comprised of regionally distinct gene expression programs that resemble cerebral vascular development and homeostasis. Our results shed light on pathways underlying SFT biology in comparison to other central nervous system tumors and provide a framework for integrating single-cell and spatial transcriptomic data from human cancers and normal tissues.

Supervised machine learning algorithms demonstrate proliferation index correlates with long-term recurrence after complete resection of WHO grade I meningioma.

OBJECTIVE: Meningiomas are the most common primary intracranial tumor, and resection is a mainstay of treatment. It is unclear what duration of imaging follow-up is reasonable for WHO grade I meningiomas undergoing complete resection. This study examined recurrence rates, timing of recurrence, and risk factors for recurrence in patients undergoing a complete resection (as defined by both postoperative MRI and intraoperative impression) of WHO grade I meningiomas. METHODS: The authors conducted a retrospective, single-center study examining recurrence risk for adult patients with a single intracranial meningioma that underwent complete resection. Uni- and multivariate nominal logistic regression and Cox proportional hazards analyses were performed to identify variables associated with recurrence and time to recurrence. Two supervised machine learning algorithms were then implemented to confirm factors within the cohort that were associated with recurrence. RESULTS: The cohort consisted of 823 patients who met inclusion criteria, and 56 patients (6.8%) had recurrence on imaging follow-up. The median age of the cohort was 56 years, and 77.4% of patients were female. The median duration of head imaging follow-up for the entire cohort was 2.7 years, but for the subgroup of patients who had a recurrence, the median follow-up was 10.1 years. Estimated 1-, 5-, 10-, and 15-year recurrence-free survival rates were 99.8% (95% confidence interval [CI] 98.8%-99.9%), 91.0% (95% CI 87.7%-93.6%), 83.6% (95% CI 78.6%-87.6%), and 77.3% (95% CI 69.7%-83.4%), respectively, for the entire cohort. On multivariate analysis, MIB-1 index (odds ratio [OR] per 1% increase: 1.34, 95% CI 1.13-1.58, p = 0.0003) and follow-up duration (OR per year: 1.12, 95% CI 1.03-1.21, p = 0.012) were both associated with recurrence. Gradient-boosted decision tree and random forest analyses both identified MIB-1 index as the main factor associated with recurrence, aside from length of imaging follow-up. For tumors with an MIB-1 index < 8, recurrences were documented up to 8 years after surgery. For tumors with an MIB-1 index ≥ 8, recurrences were documented up to 12 years following surgery. CONCLUSIONS: Long-term imaging follow-up is important even after a complete resection of a meningioma. Higher MIB-1 labeling index is associated with greater risk of recurrence. Imaging screening for at least 8 years in patients with an MIB-1 index < 8 and at least 12 years for those with an MIB-1 index ≥ 8 may be needed to detect long-term recurrences.

MerlinS13 phosphorylation controls meningioma Wnt signaling and magnetic resonance imaging features.

Meningiomas are the most common primary intracranial tumors and are associated with inactivation of the tumor suppressor NF2/Merlin, but one-third of meningiomas retain Merlin expression and typically have favorable clinical outcomes. Biochemical mechanisms underlying Merlin-intact meningioma growth are incompletely understood, and non-invasive biomarkers that predict meningioma outcomes and could be used to guide treatment de-escalation or imaging surveillance of Merlin-intact meningiomas are lacking. Here we integrate single-cell RNA sequencing, proximity-labeling proteomic mass spectrometry, mechanistic and functional approaches, and magnetic resonance imaging (MRI) across meningioma cells, xenografts, and human patients to define biochemical mechanisms and an imaging biomarker that distinguish Merlin-intact meningiomas with favorable clinical outcomes from meningiomas with unfavorable clinical outcomes. We find Merlin drives meningioma Wnt signaling and tumor growth through a feed-forward mechanism that requires Merlin dephosphorylation on serine 13 (S13) to attenuate inhibitory interactions with ß-catenin and activate the Wnt pathway. Meningioma MRI analyses of xenografts and human patients show Merlin-intact meningiomas with S13 phosphorylation and favorable clinical outcomes are associated with high apparent diffusion coefficient (ADC) on diffusion-weighted imaging. In sum, our results shed light on Merlin posttranslational modifications that regulate meningioma Wnt signaling and tumor growth in tumors without NF2/Merlin inactivation. To translate these findings to clinical practice, we establish a non-invasive imaging biomarker that could be used to guide treatment de-escalation or imaging surveillance for patients with favorable meningiomas.

Hedgehog target genes regulate lipid metabolism to drive basal cell carcinoma and medulloblastoma.

Hedgehog (Hh) signaling is essential for development, homeostasis, and regeneration1. Misactivation of the Hh pathway underlies medulloblastoma, the most common malignant brain tumor in children, and basal cell carcinoma (BCC), the most common cancer in the United States2. Primary cilia regulate Hh signal transduction3, but target genes that drive cell fate decisions in response to ciliary ligands or oncogenic Hh signaling are incompletely understood. Here we define the Hh gene expression program using RNA sequencing of cultured cells treated with ciliary ligands, BCCs from humans, and Hh-associated medulloblastomas from humans and mice (Fig. 1a). To validate our results, we integrate lipidomic mass spectrometry and bacterial metabolite labeling of free sterols with genetic and pharmacologic approaches in cells and mice. Our results reveal novel Hh target genes such as the oxysterol synthase Hsd11ß1 and the adipokine Retnla that regulate lipid metabolism to drive cell fate decisions in response to Hh pathway activation. These data provide insights into cellular mechanisms underlying ciliary and oncogenic Hh signaling and elucidate targets to treat Hh-associated cancers.

Spatial genomic, biochemical, and cellular mechanisms drive meningioma heterogeneity and evolution.

Intratumor heterogeneity underlies cancer evolution and treatment resistance1-5, but targetable mechanisms driving intratumor heterogeneity are poorly understood. Meningiomas are the most common primary intracranial tumors and are resistant to all current medical therapies6,7. High-grade meningiomas cause significant neurological morbidity and mortality and are distinguished from low-grade meningiomas by increased intratumor heterogeneity arising from clonal evolution and divergence8. Here we integrate spatial transcriptomic and spatial protein profiling approaches across high-grade meningiomas to identify genomic, biochemical, and cellular mechanisms linking intratumor heterogeneity to the molecular, temporal, and spatial evolution of cancer. We show divergent intratumor gene and protein expression programs distinguish high-grade meningiomas that are otherwise grouped together by current clinical classification systems. Analyses of matched pairs of primary and recurrent meningiomas reveal spatial expansion of sub-clonal copy number variants underlies treatment resistance. Multiplexed sequential immunofluorescence (seqIF) and spatial deconvolution of meningioma single-cell RNA sequencing show decreased immune infiltration, decreased MAPK signaling, increased PI3K-AKT signaling, and increased cell proliferation drive meningioma recurrence. To translate these findings to clinical practice, we use epigenetic editing and lineage tracing approaches in meningioma organoid models to identify new molecular therapy combinations that target intratumor heterogeneity and block tumor growth. Our results establish a foundation for personalized medical therapy to treat patients with high-grade meningiomas and provide a framework for understanding therapeutic vulnerabilities driving intratumor heterogeneity and tumor evolution.

Glioma-neuronal circuit remodeling induces regional immunosuppression.

Neuronal activity-driven mechanisms impact glioblastoma cell proliferation and invasion 1-7 , and glioblastoma remodels neuronal circuits 8,9 . Distinct intratumoral regions maintain functional connectivity via a subpopulation of malignant cells that mediate tumor-intrinsic neuronal connectivity and synaptogenesis through their transcriptional programs 8 . However, the effects of tumor-intrinsic neuronal activity on other cells, such as immune cells, remain unknown. Here we show that regions within glioblastomas with elevated connectivity are characterized by regional immunosuppression. This was accompanied by different cell compositions and inflammatory status of tumor-associated macrophages (TAMs) in the tumor microenvironment. In preclinical intracerebral syngeneic glioblastoma models, CRISPR/Cas9 gene knockout of Thrombospondin-1 (TSP-1/ Thbs1 ), a synaptogenic factor critical for glioma-induced neuronal circuit remodeling, in glioblastoma cells suppressed synaptogenesis and glutamatergic neuronal hyperexcitability, while simultaneously restoring antigen-presentation and pro-inflammatory responses. Moreover, TSP-1 knockout prolonged survival of immunocompetent mice harboring intracerebral syngeneic glioblastoma, but not of immunocompromised mice, and promoted infiltrations of pro-inflammatory TAMs and CD8+ T-cells in the tumor microenvironment. Notably, pharmacological inhibition of glutamatergic excitatory signals redirected tumor-associated macrophages toward a less immunosuppressive phenotype, resulting in prolonged survival. Altogether, our results demonstrate previously unrecognized immunosuppression mechanisms resulting from glioma-neuronal circuit remodeling and suggest future strategies targeting glioma-neuron-immune crosstalk may open up new avenues for immunotherapy.

Hypermitotic meningiomas harbor DNA methylation subgroups with distinct biological and clinical features.

BACKGROUND: Meningiomas, the most common primary intracranial tumors, can be separated into 3 DNA methylation groups with distinct biological drivers, clinical outcomes, and therapeutic vulnerabilities. Alternative meningioma grouping schemes using copy number variants, gene expression profiles, somatic short variants, or integrated molecular models have been proposed. These data suggest meningioma DNA methylation groups may harbor subgroups unifying contrasting theories of meningioma biology. METHODS: A total of 565 meningioma DNA methylation profiles from patients with comprehensive clinical follow-up at independent discovery (n = 200) or validation (n = 365) institutions were reanalyzed and classified into Merlin-intact, Immune-enriched, or Hypermitotic DNA methylation groups. RNA sequencing from the discovery (n = 200) or validation (n = 302) cohort were analyzed in the context of DNA methylation groups to identify subgroups. Biological features and clinical outcomes were analyzed across meningioma grouping schemes. RESULTS: RNA sequencing revealed differential enrichment of FOXM1 target genes across two subgroups of Hypermitotic meningiomas. Differential expression and ontology analyses showed the subgroup of Hypermitotic meningiomas without FOXM1 target gene enrichment was distinguished by gene expression programs driving macromolecular metabolism. Analysis of genetic, epigenetic, gene expression, or cellular features revealed Hypermitotic meningioma subgroups were concordant with Proliferative or Hypermetabolic meningiomas, which were previously reported alongside Merlin-intact and Immune-enriched tumors using an integrated molecular model. The addition of DNA methylation subgroups to clinical models refined the prediction of postoperative outcomes compared to the addition of DNA methylation groups. CONCLUSIONS: Meningiomas can be separated into three DNA methylation groups and Hypermitotic meningiomas can be subdivided into Proliferative and Hypermetabolic subgroups, each with distinct biological and clinical features.

NOTCH3 drives meningioma tumorigenesis and resistance to radiotherapy.

Meningiomas are the most common primary intracranial tumors1-3. Treatments for patients with meningiomas are limited to surgery and radiotherapy, and systemic therapies remain ineffective or experimental4,5. Resistance to radiotherapy is common in high-grade meningiomas6, and the cell types and signaling mechanisms driving meningioma tumorigenesis or resistance to radiotherapy are incompletely understood. Here we report NOTCH3 drives meningioma tumorigenesis and resistance to radiotherapy and find NOTCH3+ meningioma mural cells are conserved across meningiomas from humans, dogs, and mice. NOTCH3+ cells are restricted to the perivascular niche during meningeal development and homeostasis and in low-grade meningiomas but are expressed throughout high-grade meningiomas that are resistant to radiotherapy. Integrating single-cell transcriptomics with lineage tracing and imaging approaches across mouse genetic and xenograft models, we show NOTCH3 drives tumor initiating capacity, cell proliferation, angiogenesis, and resistance to radiotherapy to increase meningioma growth and reduce survival. An antibody stabilizing the extracellular negative regulatory region of NOTCH37,8 blocks meningioma tumorigenesis and sensitizes meningiomas to radiotherapy, reducing tumor growth and improving survival in preclinical models. In summary, our results identify a conserved cell type and signaling mechanism that underlie meningioma tumorigenesis and resistance to radiotherapy, revealing a new therapeutic vulnerability to treat meningiomas that are resistant to standard interventions.