Pilocytic Research Articles

Increased SOX10, p16, and Cyclin D1 Immunoreactivity Differentiates MAP Kinase-activated Low-grade Gliomas From Piloid Gliosis.

Low-grade gliomas and reactive piloid gliosis can present with overlapping features on conventional histology. Given the large implications for patient treatment, there is a need for effective methods to discriminate these morphologically similar but clinically distinct entities. Using routinely available stains, we hypothesize that a limited panel including SOX10, p16, and cyclin D1 may be useful in differentiating mitogen-activated protein (MAP) kinase-activated low-grade gliomas from piloid gliosis. Reviewers blinded to clinical and pathologic data reviewed and quantified immunohistochemical expression patterns across 20 cases of piloid gliosis and 37 cases of MAP kinase-activated low-grade gliomas, including pilocytic astrocytoma and ganglioglioma. The majority of MAP kinase-activated low-grade glioma cases demonstrated extensive immunoreactivity for at least 2 of the 3 immunohistochemical markers, whereas none of the gliosis cases demonstrated significant immunoreactivity for more than one individual immunohistochemical marker. SOX10 and p16 demonstrated the highest individual sensitivity whereas cyclin D1 demonstrated the highest individual specificity to discriminate neoplastic from nonneoplastic cases in this cohort. A composite panel score based on significant immunoreactivity of at least 2 of the 3 markers provided specificity and a positive predictive value of 100% in differentiating MAP kinase-activated low-grade glioma from gliosis, as 0/20 (0%) of gliosis cases were scored positive compared with 24/37 (65%) of MAP kinase-activated low-grade glioma cases. We conclude that while the immunoreactivity of these markers may be suggestive of a low-grade glioma diagnosis, SOX10, p16, and cyclin D1 should be applied in combination to maximize diagnostic value.

ASTROCYTOMA OF THE CERVICAL SPINAL CORD IN AN INFANT WITH TORTICOLLIS

The relevance of the problem is determined by the rather high prevalence of central nervous system (CNS) tumors in children and the need for oncologic vigilance. The presentation of the clinical case illustrates the need for careful analysis of the initial clinical signs, which are usually nonspecific and may resemble symptoms of other diseases. A case from practice describes the timely diagnosis of pilocytic astrocytoma in a child of the first year of life with torticollis as the debut of the disease. The diagnosis was made on the basis of a thorough clinical, neurological, and immunohistochemical examination and the use of neuroimaging techniques with the goal of further surgical, medical, and radiation treatment. The aim of the work. Description of a clinical case of astrocytoma of the cervical spinal cord, which manifested itself as torticollis in a child in the first year of life. Material and methods of the research. Clinical, biochemical, immunohistochemical, and imaging examination of a child of toddler age. Results of the research. A child with manifestations of torticollis at the age of eleven months was studied. Variants of congenital and acquired torticollis and inflammatory diseases of the central nervous system were excluded. According to clinical, neurological, and neuroimaging examinations, the diagnosis was made: benign intramedullary neoplasm of the spinal cord, pilocytic astrocytoma C5-Th2. Surgical intervention was performed with partial removal of the tumor with histochemical examination, followed by restorative therapy and observation in the distant postoperative period. Conclusions. Sudden appearance of symptoms of torticollis in a child in the first year of life may indicate the presence of a CM tumor. Early diagnosis allows to provide the child with highly specialized care, perform surgical intervention, and contribute to the improvement of the general condition and quality of life.

Cerebellar pilocytic astrocytoma: predictors of recurrence based on MRI morphology—a single-centre experience

PurposeWe aimed to present our surgical experience and the impact of a solid or cystic morphology of cerebellar pilocytic astrocytoma (cPA) on surgery and the risk for a re-resection.MethodsWe retrospectively analyzed all children operated at our institution between 2009 and 2023 for cPA. Tumours were categorized into 4 groups: (i) cystic PA without cyst wall enhancement, (ii) cystic PA with cyst wall enhancement, (iii) solid tumour, (iv) and solid tumour with central necrosis.ResultsForty-two children with a median age at surgery of 7.1 years (range 0.7–14 years; male to female ratio 1.5) were identified. The median follow-up time was 3.1 years (0.6–14 years). Twenty-eight patients (66.6%) presented with cystic PA (20 without and 8 with cyst wall enhancement), 9 patients (21.4%) exhibited a solid tumour with central necrosis and 5 (11.9%) had a solid tumour without central necrosis. Gross total resection could be achieved in 31 patients (73.8%), near total resection in 6 (14.3%), and subtotal resection in 5 (11.9%). Progression occurred in 11 cases with 9 patients having a 2nd resection after a mean time of 3.4 years. The highest risk for a 2nd resection was seen in the group of solid tumours with a necrotic centre (odds ratio = 2.3), progression of enhancing cyst wall remnants was seen in one out of two patients with remnants needing reoperation.ConclusionSurgery in cerebellar PA should aim for gross total resection of the solid-enhancing tumour.

A bibliometric analysis of research trends and hotspots of pilocytic astrocytoma from 2004 to 2023

Pilocytic astrocytoma (PA) is a WHO grade I neoplasm with a favorable prognosis. It is the most common pediatric benign tumor. Recently, PA has attracted more and more attention and discussion from scholars. The aim of this study is to comprehensively generalize the evolution of this field over the past two decades through bibliometric analysis and to predict future research trends and hotspots. The literature over the last two decades (2004–2023) related to PA was obtained from the Web of Science Core Collection (WoSCC) database. Bibliometric analyses were conducted based on the following aspects: (1) Annual publication trends; (2) Publications, citations/co-citations of different countries/institutions/journals/authors; (3) the map of Bradford’s Law and Lotka’s Law for core journals and author productivity; (4) Co-occurrence, cluster, thematic map analysis of keywords. All analyses were performed on VOSviewer and R bibliometrix package, and Excel 2024. Our results showed that research on PA displayed a considerable development trend in the past 20 years. The USA had a leading position in terms of scientific outputs and collaborations. Meanwhile, German Cancer Research Center contributed the most publications. Child's Nervous System had the highest number of publications and Acta Neuropathologica was the most co-cited journal on this subject. Gutmann, D.H. and Louis, D.N. were the authors with the most articles and co-citations in this field. The research emphases were molecular mechanisms, neurofibromatosis, pilomyxoid astrocytoma, differential diagnosis, and therapy. We systematically analyzed the literature on PA from a bibliometric perspective. The demonstrated results of the knowledge mapping would provide valuable insights into the global research landscape.

Circumscribed Pilocytic Astrocytoma Including Pilomyxoid and Intermediate Pilomyxoid Variants — A Single Institutional, Retrospective Study

Circumscribed Pilocytic Astrocytoma Including Pilomyxoid and Intermediate Pilomyxoid Variants — A Single Institutional, Retrospective Study

CLASSIFICATION WITH MACHINE LEARNING METHODS FROM MULTI-SEQUENCE MR IMAGES OF CHILDHOOD POSTERIOR FOSSA TUMORS

Childhood brain tumors rank high among the leading causes of mortality, being the second most common type of cancer after leukemia. Abnormal structures in the brain are visualized using MRI techniques, which are the most commonly employed tools for distinguishing the neural structure of the human brain. However, identifying and diagnosing these abnormal structures can be a time-consuming and critical process. In this study, tumors in the Magnetic Resonance images of patients with Posterior Fossa tumors were segmented using two different image segmentation methods. Subsequently, numerical features were extracted from these tumors, and significant numerical features among tumor groups were determined using the Student's T-test; based on these features, tumor types were classified using machine learning algorithms. The study focused on the three most common types of Posterior Fossa tumors: Medulloblastoma, Ependymoma, and Pilocytic Astrocytoma, utilizing T2, Contrast-Enhanced T1, and ADC sequences. A total of forty-eight different numerical features were extracted from the segmented tumors and then acquired significant features were classified using five different machine learning algorithms. Among PA-MB, EM-MB and EM-PA tumor types, the average result of the most successful method in the T1 sequence was 86.93%, while it was 93.7% for the T2 sequence and 92.06% for the ADC sequence. Decision tree, SVM and Ensemble classifiers gave more successful results than others. As a result of the detailed examination, our study not only makes valuable contributions to the literature, but also has a promising structure in terms of its potential to help clinicians.

Septum pellucidum pilocytic astrocytoma: case report and literature review

IntroductionSeptum pellucidum pilocytic astrocytoma is rare. There are only 3 reported cases in literature. Our patient is the fourth case.Case presentationA 17-year-old male presented with headache. CT brain and MRI brain showed septum pellucidum lesion with obstructive hydrocephalus which looked like colloid cyst. Intraoperatively, the tumor was attached to the lower part of septum pellucidum and it didn’t look like a colloid cyst. Histopathology was pilocytic astrocytoma. Postoperatively, patient recovered well with no neurological deficits or adverse neurological sequalae.ConclusionSeptum pellucidum pilocytic astrocytoma should be considered as one of the differential diagnosis of septum pellucidum tumors. We observed that the interhemispheric transcallosal transventricular approach might be associated with lesser comorbidities and neurological deficits in tumors in this location.

Gamma Knife Radiosurgery for symptomatic eloquently deep-seated cystic pilocytic astrocytoma mural nodules: Retrospective case series of effective outcomes.

Although most pilocytic astrocytomas grow slowly, their progression in critical sites such as the brainstem or hypothalamus may prove fatal much more rapidly. Cystic progression may be more problematic than solid tumor. Patients with progressive cystic PAs located in eloquent deep areas of the brain are the best candidates for stereotactic radiosurgery. This retrospective case series aims to present the effective outcomes obtained from GKRS, targeting the mural nodules of symptomatic eloquently deep-seated cystic PAs in 9 consecutive patients treated at the IMC Gamma Knife Centre in Cairo, Egypt, between 2003 and 2021. The median follow-up period was 84months (range 24-240months). The median treated mural nodule volume was 1.25 cm3 (range 0.32-1.97 cm3), treated with a median peripheral prescription dose of 12Gy and a median maximum dose of 24Gy. The median cyst volume in treated patients was 7.64cm3(range 1.66-40.6cm3). At the last follow-up, 7 out of 9 patients (78%) achieved tumor control (marked reduction > 50% of the entire tumor volume in 6 patients and moderate tumor reduction < 50% in one patient) in addition to clinical improvement. The median time of confirmed tumor reduction was 18months (range 12-32months). Two patients reported progression of the treated tumor. The overall tumor control rates at 2, 5, and 7years of follow-up were 88.9%, 78%, and 78%, respectively. The encouraging results of this series indicate that limiting the GKRS to the mural nodule of eloquently deep-seated cystic PAs may be a practical and effective pattern in the salvage of its treatment. Our data do not support radiation for extensive, large symptomatic cysts in deep-seated cystic PA or patients where microsurgical removal is feasible.

CNSC-43. NEUROTRANSMITTER DEPENDENCY UNDERLIES TUMOR GROWTH IN HUMANIZED PEDIATRIC LOW-GRADE GLIOMA MODELS

Abstract Brain tumors arise in close association with neurons, suggesting that these non-neoplastic cells may be critical stromal drivers of brain tumor initiation and growth. Previously, we have shown that murine low-grade optic glioma formation and progression in the setting of Neurofibromatosis type 1 (NF1) is dictated by neurons and neuronal activity. In these studies, these neuronal dependencies reflected neuronal activity-driven enzymatic cleavage of a growth factor (neuroligin-3) from oligodendrocyte precursors cells (tumor initiation) or neuronal production of a paracrine factor to stimulate T cell support of optic glioma growth (tumor progression). Since neurons typically communicate with other neurons through neurotransmitters, we sought to explore the possibility that neurotransmitters operate to modulate low-grade glioma growth using humanized mouse models of pilocytic astrocytoma (PA). Leveraging single cell RNA sequencing of three independent sets of pediatric PAs, we identified neurotransmitter pathway enrichment in the tumor cells. This neurotransmitter pathway enrichment reflected aberrant expression of specific neurotransmitter receptors, which we confirmed in three independently generated PA tissue microarrays and in five distinct primary PA cell lines grown in vitro. Moreover, this aberrant neurotransmitter receptor expression established differential neurotransmitter PA growth dependencies in vitro. Importantly, interruption of neurotransmitter signaling in human PA xenografts attenuated tumor growth and ERK activation in Rag1-/- mice in vivo. Finally, we discovered crosstalk between neurotransmitter receptor and receptor tyrosine kinase signaling that revealed another target for therapeutic inhibition. Taken together, these findings elucidate a previously unknown neurotransmitter PA growth dependency amenable to therapeutic targeting.

EXTH-11. PEDIATRIC GLIOMA IMMUNE PROFILING IDENTIFIES TIM3 AS A THERAPEUTIC TARGET IN BRAF-FUSION PILOCYTIC ASTROCYTOMA

Abstract Despite being the leading cause of childhood mortality, pediatric gliomas have been relatively understudied. Repurposing of adult brain tumor immunotherapies in pediatric patients has not been successful, highlighting the need for pediatric-specific immunotherapies. Pilocytic astrocytomas (PA) are the most common pediatric glioma. While surgical resection of PA is the first-line treatment, the ten-year progression-free survival rate for patients with residual tumors is &amp;lt;50%. Notably, some PAs undergo spontaneous regression after partial resection, suggesting potential baseline tumor immunoreactivity. Whole transcriptome sequencing performed on a commercial platform of pediatric gliomas (n=250) showed that MAPK-driven gliomas have higher interferon signatures compared to other molecular subgroups. Single-cell sequencing identified a unique activated and cytotoxic microglia population designated MG-Act in BRAF-fused MAPK-activated PA (n=13; p &amp;lt; 0.05), but not in pediatric high-grade gliomas (n=5) or normal brain (n=3). TIM3 was expressed on the luminal side of endothelial cells and MG-Act, but not in the surrounding normal brain based on sequential multiplex imaging. Flow cytometry showed that TIM3 intensity is upregulated on immune cells in the PA tumor microenvironment (TME) relative to matched peripheral blood immune cells (n=6; p &amp;lt; 0.01). Anti-TIM3 reprogrammed fresh ex vivo immune cells from the TME of human PAs (n=3) to a pro-inflammatory cytotoxic phenotype. In a genetically engineered murine model of MAPK-driven low-grade gliomas, median survival (MS) was 252 days in mice treated with anti-TIM3 (n=21; p&amp;lt;0.01) relative to IgG control (MS: 110 days; n=20) or anti-PD-1 (MS: 134 days; n=20). The therapeutic activity of anti-TIM3 was abrogated in the CX3CR1 microglia knockout background. ScRNA sequencing data during the therapeutic window of anti-TIM3 in wild-type mice demonstrated enrichment of the MG-Act population within low-grade gliomas at two different longitudinal time points but not in IgG-treated controls. Together, these data indicate that anti-TIM3 should be considered for clinical trials in pediatric low-grade MAPK-driven gliomas.

CNSC-03. HIGH EXPRESSION OF PICCOLO AND SYNTAXIN-1A IN PAEDIATRIC MEDULLOBLASTOMA DUE TO BOTH: HIGH NEURONAL FRACTION AND ENDOGENOUS EXPRESSION

Abstract Emerging evidence indicates that the “healthy” nervous system contributes to the pathogenesis of cancer. Tumor cells were found to form ultra-long protrusions with distinct synapses, mainly in the infiltrative zone, resulting in a neuron-to-brain tumor synaptic communication. Located at the presynapse, proteins of the cytomatrix of the active zone have been identified to maintain highly specialized functions in neurons. Further, the proteins were shown to be involved in progression in various tumors, but little is known about their role in brain tumors. This study examined the expression of CAZ proteins in glioma and medulloblastoma. Tumor samples of Astrocytoma, glioblastoma, pilocytic astrocytoma and medulloblastoma were obtained during neurosurgical resection. Transcription rate of following CAZ proteins was measured via qPCR: SNAP25, VAMP1, VAMP2, SYT1, PCLO, BSN, STX1A. To examine amount of neuronal tissue TUBB3 and for glial fraction GFAP were quantified. A medulloblastoma cell line (DAOY) was furthermore analyzed to evaluate origin of high expressed proteins. Medulloblastoma showed high expression of PCLO (pilocytic astrocytoma vs. medulloblastoma p=0.0126) and STX1A (pilocytic astrocytoma vs. medulloblastoma p=0.0006) compared to. Likewise a high transcriptional level of TUBB3 could be seen with significance to pilocytic astrocytoma (2.2 ± 1.4 vs. 0.2 ± 0.17; p = 0.0018), which could indicate a high amount of neuronal tissue in given medulloblastoma samples. To rule out a causal link between high proportion of neuronal tissue and high CAZ expression, a paediatric medulloblastoma cell line was analysed. High expression of PCLO and STX1A in absence of TUBB3 was shown (3.8 and 2.01 vs. 0.059), indicating endogenous expression of CAZ proteins in medulloblastoma.

PATH-14. UTILITY OF DNA METHYLATION ANALYSIS IN HISTOLOGICALLY-CONFIRMED PA PATIENTS WITH POOR PROGNOSIS

Abstract INTRODUCTION Pilocytic astrocytoma (PA) is a circumscribed low-grade astrocytic glioma, generally considered to be associated with a good prognosis. However, some PA patients experience unfavorable outcomes; advanced age was known as an independent poor prognostic factor. This study retrospectively reviewed PA patients and conducted molecular analyses for elderly patients. METHODS We analyzed data from 29 histologically confirmed PA patients treated at a single center from 2002 to 2021 and conducted integrated molecular analyses including DNA methylation profiling for elderly PA patients. RESULTS The median age at diagnosis was 14 years (range 3-82 years), with 4 patients (14%) being elderly (patients≥60years old). Elderly patients had significantly worse progression-free survival and overall survival. DNA methylation analysis was performed on 2 of the 4 elderly patients. Despite histological diagnoses of PA, methylation profiling classified one case as high-grade astrocytoma with piloid features (methylation class scores below 0.3 in both v11b4 and v12.5) and the other as glioblastoma, IDH-wildtype (score over 0.5 in both v11b4 and v12.5), using classifiers from the German Cancer Research Center and t-SNE analysis. CONCLUSION Elderly patients with PA morphology showed unfavorable outcomes in this cohort. In those patients, DNA methylation profiling revealed the possibility of high-grade astrocytic tumors, including newly defined entities.

CNSC-41. DABRAFENIB AND TRAMETINIB AS A PROMISING TREATMENT OPTION FOR PEDIATRIC POPULATION WITH LOW-GRADE GLIOMAS THAT HAVE BRAF V600E MUTATION:A BREAKTHROUGH IN THE FIELD OF NEURO- ONCOLOGY

Abstract Two-thirds of all pediatric malignant central nervous tumors, including high-grade (glioblastoma, anaplastic astrocytoma) and low-grade (ganglioglioma, pilocytic astrocytoma) carcinomas, are gliomas. Low-grade glioma(LGG) exhibits genetic alterations caused by the BRAF kinase mutation, such as replacing glutamic acid (E) in place of valine (V) at the 600 positions, known as the V600E point mutation. Pediatric low-grade gliomas (PLGGs) also comprise around one-third of juvenile brain tumors and are the most frequent central nervous system tumors. Patients were randomized 2:1 to dabrafenib plus trametinib (D+T) or carboplatin plus vincristine (C+V). Where possible, complete surgical removal is the mainstay of treatment for progressing or symptomatic PLGG.Radiation therapy has historically been used to treat PLGG in both up-front and salvage scenarios. To delay or avoid the necessity for radiation therapy in young children with advancing or incompletely resected PLGG, chemotherapy was created in 1980. On March 16, 2023, the Food and Drug Administration approved the use of trametinib (Mekinist, Novartis) with dabrafenib (Tafinlar, Novartis) in pediatric patients suffering from low-grade glioma (LGG) who require systemic therapy and are at least one year old. Nevertheless, early-stage clinical trials have produced encouraging results that may revolutionize the treatment of LGG in the near future.

PATH-11. TECTAL GLIOMA: CLINICAL, PATHOLOGICAL, AND MOLECULAR FEATURES

Abstract Tectal glioma (TG) is a rare lower-grade glioma (LrGG) that occurs in the tectum, mainly affecting children. The clinical course is usually indolent, with common symptoms including headache, gait disturbance, and ataxia resulting from obstructive hydrocephalus. TG shares pathological similarities with pilocytic astrocytoma (PA), but recent genetic analyses have revealed distinct features, such as alterations in KRAS and BRAF. Here, we report the clinical, radiological, pathological, and molecular characteristics of TG cases in our hospital. We conducted a retrospective review of cases clinically diagnosed as TG and surgically treated at our institute between January 2005 and March 2023. Molecular analysis, including genome-wide DNA methylation profiling, was performed. Six cases were identified and the median age at diagnosis was 30.5 years (range: 6–45 years). The mean tumor diameter was 22.8 mm (range: 14.7–33.2 mm), with obstructive hydrocephalus observed in all cases. Contrast enhancement of the tumor was noted in four cases and cyst formation occurred in two cases. Four patients underwent biopsy or biopsy with endoscopic third ventriculostomy, and two patients underwent tumor resection. Postoperatively, three patients received radiotherapy and two were treated with chemotherapy. The median overall survival was 6.2 years (range: 1.4–7.3 years), and the median progression-free survival was 3.4 years (range: 1.4–7.3 years). Histological diagnoses included three cases of PA, one case of astrocytoma, and two cases of high-grade glioma. Among the three patients who underwent molecular evaluation, including genome-wide methylation analysis, two had KRAS mutation and one had H3-3A K27M mutation. Our results demonstrate the diverse histological and molecular characteristics of TG distinct from other LrGGs. Given the heterogeneous pathological background and the risk of pathological progression in TG, we emphasize the importance of comprehensive diagnosis, including molecular evaluation.

BIOM-55. SENSITIVITY OF IMMUNOHISTOCHEMISTRY WITH BRAF VE1 ANTIBODY FOR BRAF V600E IN PRIMARY CENTRAL NERVOUS SYSTEM TUMORS

Abstract BACKGROUND BRAF gene encodes for a key protein of the RAS-RAF-MEK-ERK pathway. BRAF alterations are found in a variety of primary central nervous system (CNS) tumors ranging from 3% of glioblastomas to 60% of pleomorphic xanthoastrocytomas. BRAF V600E mutation is the most common BRAF alteration found in CNS malignancies, and it has been successfully targeted with BRAF/MEK inhibitors. Novel BRAF inhibitors, still in development, have shown promising antitumor activity. Next-generation sequencing (NGS) has become a standard test in the era of histo-molecular diagnosis, but it can be unavailable or inaccessible, and results usually take longer. Immunohistochemistry (ICH) with VE1 antibody for BRAF V600E protein has shown high discordant results with sequencing in other tumor types. We aimed to establish the concordance of BRAF VE1 and NGS sequencing in CNS tumors. METHODS Single-center retrospective analysis of patients with BRAF V600E mutant CNS tumors by NGS testing. RESULTS 30 patients with BRAF V600E mutant primary CNS tumors by NGS were included, 18 were male. 15 were classified as IDH-wildtype gliomas, 4 low grade neuroepithelial gliomas, 8 pleomorphic xanthoastrocytoma, 2 pilocytic astrocytomas and 1 papillary craniopharyngioma. IHC testing with BRAF VE1 antibody was done at the initial pathological classification in 23 of the cases being positive in 15 and negative in 8 cases. In 7 cases IHC was not done but has been requested for retrospective analysis and results are pending. Sensitivity for BRAF VE1 IHC was 65%. CONCLUSION When compared to NGS testing, ICH with BRAF VE1 antibody for BRAF V600E in CNS tumors shows modest sensitivity, being a limited tool when results are needed promptly or NGS is inaccessible. Determining specificity of the test will be crucial to establish its reliability for patient selection. Sequencing should be obtained when possible and remains the more reliable method for detecting V600E.

PATH-17. MOLECULAR CLASSIFICATION OF H3K27-WILDTYPE SPINAL CORD GLIOMAS: IMPLICATIONS FOR PROGNOSIS AND THERAPEUTICS

Abstract BACKGROUND H3K27-wildtype spinal cord gliomas (H3WT-SCGs) are rare and heterogeneous tumors that present significant challenges in pathological classification. Traditional histologic diagnoses often do not align well with the underlying molecular characteristics of these tumors. METHODS We characterized 55 cases of H3WT-SCGs using a comprehensive approach that included DNA methylation array, whole-exome sequencing, transcriptome sequencing, proteomics, and single-cell RNA sequencing. Unsupervised clustering analysis was performed to identify distinct molecular subtypes. RESULTS The analysis identified seven distinct spinal cord methylation (SCM) clusters: pilocytic astrocytomas (PA-SPINE), PA-immune enriched (PA-IME), diffuse leptomeningeal glioneuronal tumor (DLGNT), subependymoma (SUBEPN-SPINE), glioblastoma-like (GBM-like), and pleomorphic xanthoastrocytoma-like (PXA-like). There was a 61.8% discordance between SCM classes and traditional histologic diagnoses. The new molecular classification provided a better correlation with molecular features and patient prognosis. BRAF fusions were enriched in PA-SPINE and DLGNT (p = 0.04), and DLGNT showed significant chromosomal alterations, including 1p loss (p = 6.5e-08) and 1q gain (p = 3.6e-05). Notably, we identified two distinct classes of PA-SPINE: adult (older than 18 years) and pediatric. Adult PAs exhibited lower frequencies of BRAF fusions (p = 1.4e-03), shorter tumor lengths (p = 3.7e-04), and longer progression-free survival (p = 0.062). Adult PA neoplastic cells were less differentiated, with higher expression of EGFR and neuronal markers, and lower cytokine and chemokine expression compared to pediatric cases. Single-cell analysis revealed reduced infiltration of monocyte-derived macrophages and proliferative myeloid cells in adult cases. Both PA-IME and PA-pediatric clusters were characterized as immune-hot tumors with high immune cell enrichment. CONCLUSION This study defined clinically relevant molecular classes of H3WT-SCGs that better reflect patient prognosis and molecular characteristics compared to traditional histologic diagnoses. The findings suggest potential therapeutic implications, especially in immune-hot tumors like IME and PA-pediatric, which could benefit from targeted immunotherapies.

CSIG-29. BRAF INHIBITOR THERAPY IN BRAF-MUTATED PRIMARY BRAIN TUMORS: A SINGLE-CENTER EXPERIENCE

Abstract BACKGROUND BRAF pathway alterations are frequent in glial/neuroepithelial tumors. BRAF-targeted therapy with BRAF inhibitors (BRAFi) and/or MEK inhibitors (MEKi) has proven efficacy in clinical trials, though mainly enrolling pediatric patients. We sought to investigate real-world data for adult patients with BRAF-pathway mutant glial/neuroepithelial neoplasms treated with BRAFi/MEKi. METHODS Adults with BRAF-pathway mutated glial/neuroepithelial neoplasms treated with BRAFi/MEKi were retrospectively reviewed. RESULTS Five patients (n=4 female, median age at diagnosis 36) were identified (tumor types: glioblastoma n=1, high-grade astrocytoma with epithelioid features n=1, low-grade neuroepithelial tumor n=1, pilocytic astrocytoma n=1, pleomorphic xanthoastrocytoma n=1). Four had BRAF V600E and one had NF1 p.S2687Cfs*5 mutant tumors. Prior to targeted therapy initiation, patients underwent a median 2.4 treatments including surgery (n=4), radiation therapy (n=4), chemotherapy (temozolomide n=4; carboplatin/vincristine n=1). BRAF-targeted therapies included dabrafenib/trametinib (n=4), binimetinib/encorafenib (n=2), binimetinib (n=2). One NF1-mutant glioblastoma received binimetinib followed by binimetinib/bevacizumab. Median BRAFi/MEKi treatment was 15.2 months (range: 6-36 months). Toxicities included leukopenia (n=3), peripheral edema (n=1), reduced ejection fraction (n=1), skin rash (n=5), transaminitis (n=1) with all patients requiring dose reductions and 3 cases requiring discontinuation. Among patients where BRAFi/MEKi was discontinued due to toxicity, 2 received other treatments at progression, then switched to a different BRAFi/MEKi combination, which they tolerated (duration 6-10months). Best radiographic response was partial response, noted in 3 patients treated with dabrafenib/trametinib. Four patients remain alive and continue BRAFi/MEKi. CONCLUSIONS In this cohort of heavily-pretreated patients with glial/neuroepithelial neoplasms, BRAF-targeted therapy was associated with durable responses. Interestingly, two patients who were unable to tolerate one combination of BRAFi/MEKi were able to tolerate a different combination with sustained response. Our findings support ongoing use of BRAF targeted therapy for CNS tumors. Optimal timing and duration of treatment requires further prospective evaluation in adult patients.

CNSC-58. BIOPROCESSING OF VIABLE SURGICAL PEDIATRIC BRAIN TUMOR SPECIMENS FOR GENOME-GUIDED PERSONALIZED DRUG TESTING

Abstract Novel treatment approaches are urgently needed for pediatric central nervous system (CNS) tumors as they are the leading cause of cancer-related deaths in children. A lack of research materials impedes progress towards developing such therapies. Although various brain cancer biobanks exist, these rarely store viable patient-derived tissue and cells for live cell analyses, including cell fate assays and testing for drug sensitivities. We propose that a biorepository of viable cell dissociates and tissue broadly representing CNS tumor entities overcomes these limitations. From a combination of molecular diagnoses and histopathologic assessment of over 120 samples collected, we generated a biorepository of roughly 35 distinct entities of pediatric CNS tumors in our Stanford neuro-bioprocessing cohort. Based on the Central Brain Tumor Registry of the United States, the proportion of subtypes represented in our cohort match that of the general population with exceptions. We established a standardized bioprocessing pipeline that can be used as a template for tissue collection and model development in the broader disease context and for multiple downstream applications. Our emphasis on cryostorage of viable cells and tissue facilitates ad hoc live cell analyses. In addition to gaining a better understanding of tumor pathophysiology, we attempted a rapid bed-to-bench-to-bedside approach using comparative RNA expression profile analyses in an individual patient’s pilocytic astrocytoma. Novel drug targets were identified by analyzing RNA transcripts that are highly expressed (outliers) compared with a compendium of 12,747 brain and non-brain tumor samples. We validated outliers as drug targets using acute cell isolates, and identified a novel target in recurrent low-grade glioma. These studies illustrate that biobanking of viable patient-derived material enables developing personalized therapies with the goal of improving patient outcomes. As demonstrated here, patient-derived acute cell isolates facilitate identifying drug vulnerability, creating an opportunity for more personalized treatment of patients with CNS tumors.

SURG-40. PEDIATRIC LOWER GRADE GLIOMA SURGERY IN THE ERA OF GENOMIC MEDICINE

Abstract INTRODUCTION In the 2021 WHO Brain Tumor Classification, pediatric-type gliomas are distinctly categorized from their adult counterparts. The continual evolution of cancer genomics has significantly broadened the spectrum of available treatment options. Here we would like to consider surgery for pediatric low-grade gliomas. METHODS We retrospectively analyzed 41 cases of low-grade gliomas or glioneuronal tumors in pediatric patients who underwent surgery at our institute from 2002 to 2023. We discussed surgical strategies based on molecular classification. RESULTS Among the cases, there were 34 gliomas and 7 glioneuronal tumors. According to the new WHO classification, they corresponded to 1) Adult-type diffuse gliomas, 2) Pediatric-type diffuse low-grade gliomas, 3) Circumscribed astrocytic tumors, or 4) Glioneuronal and neuronal tumors. Cases without molecular diagnosis were also considered in light of the new WHO classification. Among molecularly diagnosed astrocytomas involving the cerebral hemisphere, brain stem, spinal cord, there were no cases of 1), and 2) 3) were the main cases. It is important in surgical selection to note that these cases generally have a more favorable prognosis compared to the adult type and have usefulness in diagnosing MAPK pathway abnormalities leading to the selection of molecularly targeted drugs. 3) includes pilocytic astrocytoma, subependymal giant cell astrocytoma, and pleomorphic xanthoastrocytoma. Among these, in the treatment of pilocytic astrocytoma of the visual tract and hypothalamus, biopsy is essential for molecular diagnosis and therapeutic agent selection. 4) is mainly an epilepsy-related tumor. While their removal contributes to genetic diagnosis and epileptic seizure control, total removal may not always be deemed necessary. CONCLUSION Based on the new WHO classification, a reevaluation of treatment strategies for pediatric brain tumors is necessary.

EPID-20. PRIMARY INTRAMEDULLARY PILOMYXOID ASTROCYTOMA OF SPINAL CORD (PIPASC): A SYSTEMATIC REVIEW OF CASE REPORTS AND CASE SERIES OF TWO DECADES

Abstract BACKGROUND Pilomyxoid Astrocytoma (PMA), new variant of pilocytic astrocytoma, is more aggressive and relatively rare, mostly seen in children and commonly found in brain. Primary intramedullary pilomyxoid astrocytoma of spinal cord (PIPASC) is extremely rare. The distinct aggressive and pathological behavior, poor prognosis and the diversity in response to various treatment modalities makes the PIPASC an oncologic enigma. We aim to evaluate the clinical manifestations, histopathologic spectrum and onco-surgical management of this neoplasm. MATERIALS AND METHODS After an extensive literature search using PubMed Central and Google Scholar, eight case reports and one case series of patients with spinal PA were retrieved and included using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines without applying any filter of time, study type or place. Case presentations of 12 patients were analyzed in this review. RESULTS Pediatric preponderance of the neoplasm (75%) with the mean age of 7.90 ± 4.51 years was noted. Sensory deficits and scoliotic deformity were the most common presenting symptom and sign in 83.33% and 33.33% of patients, respectively. Thoracic spine (50%) was most commonly affected region. MRI showed the most consistent findings of cord compression in 100% cases and the lesion appeared hypointense on T1- weighted images (T1WI) and hyperintense on T2-weighted images (33.33%). The average post treatment survival duration was found to be more than 2 years. CONCLUSIONS Occurrence of PIPASC among pediatric population is rare. They have possibility of extraneural metastasis, can differentiate into more malignant glioma and get recurrent due to which they require a long-term follow-up of the patients. Further studies are required to investigate the utility of chemotherapy and radiotherapy in its management.