Central Nervous System Tumors Research Articles

BIOM-51. MOLECULAR SUBTYPES, CLINICAL CHARACTERISTICS, AND THERAPEUTIC IMPLICATIONS FOR CNS TUMORS WITHBCOR/BCORL1 FUSION/INTERNAL TANDEM DUPLICATION

Abstract Central nervous system (CNS) tumors with either BCOR internal tandem duplication (BCOR ITD) or gene fusions involving BCOR/BCORL1 (BCOR FUS) are recognized as tumor types with characteristic molecular and clinical features but lacking clear therapeutic guidance. In an extensive international effort, we compiled a retrospective cohort of 229 (148 BCOR ITD, 81 BCOR FUS) unique cases via molecular profiling of CNS tumors. By analyzing DNA methylation patterns of 220 tumors we confirmed distinct epigenetic profiles of BCOR ITD versus BCOR FUS. The majority (91 percent) of BCOR FUS primary tumors was localized in the supratentorial region whereas BCOR ITD were localized across all anatomical CNS compartments. Median patient age at diagnosis was 20 years for BCOR FUS and 4 years for BCOR ITD. Metastatic disease was rare in BCOR FUS patients but more common in BCOR ITD tumors where 10 percent presented with metastatic disease and one third showed CNS or (rarely) extra-CNS metastasis in the course of disease. This was also reflected in clinical outcome as 5-year overall survival (OS) was 89 percent in BCOR FUS but 61 percent in BCOR ITD. In contrast, 5-year progression-free survival (PFS) was comparable reaching 27 percent in BCOR FUS and 30 percent in BCOR ITD. Integrating treatment details we found a trend towards benefit of gross-total resection on OS (BCOR FUS, n=18, p<0.08; BCOR ITD, n=67, p<0.12) but not for PFS (BCOR FUS, n=16, p<0.33; BCOR ITD, n=64, p<0.59). Radiotherapy was associated with improved PFS (BCOR FUS, n=18, p<0.01; BCOR ITD, n=70, p<0.001) and OS (BCOR FUS, n=20, p<0.01; BCOR ITD, n=73, p<0.001). Further in-depth analyses of clinical outcome parameters (primary metastatic disease, radiotherapy approach, chemotherapy type, patient age) are currently ongoing. In summary, we provide first robust annotation of CNS BCOR tumor types, clinical outcomes and therapy.

BIOM-67. DIFFERENTIAL DNA METHYLATION PATTERNS IN THE CSF OF PATIENTS WITH DIFFUSE GLIOMAS

Abstract Studies have shown that different central nervous system (CNS) tumor types exhibit unique DNA methylation profiles. DNA methylation-based machine learning classification of CNS tumor tissue has been demonstrated to be highly-accurate in differentiating between tumor types, including between diffuse glioma subtypes. While similar analyses have been performed using cell-free DNA (cfDNA) from blood, few studies have looked at the potential of DNA methylation as a biomarker for diffuse gliomas using CSF-derived cfDNA. In this study, we analyzed CSF cfDNA methylation patterns in diffuse glioma patients. DNA methylation profiling of CSF of patients with glioblastoma, IDH-wildtype (GBM) (n=37), IDH-mutant diffuse gliomas (n=12), and non-neoplastic conditions (n=5) was performed using cell-free methylated DNA immunoprecipitation and high-throughput sequencing (cfMeDIP-seq). Methylation quantification was estimated for each genomic region. Significance testing was performed between diagnostic groups to discover differentially-methylated regions (DMRs). The 300 most differentially-methylated regions (DMRs) for each comparison (IDH-wildtype vs. IDH-mutant, IDH-mutant vs. control, IDH-wildtype vs. control), for a total of 900 DMRs, were utilized as features in dimensionality reduction analysis and machine learning. Out of ~1×107 defined genomic regions, there were ~7×105 DMRs between GBM and control samples and ~1.5×106 DMRs between GBM and IDH-mutant samples, accounting for ~7% and ~15% of the genome, respectively. Uniform manifold approximation and projection (UMAP) and hierarchical clustering analysis revealed that samples were mostly clustered by diagnosis. Random forest analysis of the 900 DMRs with an 80/20 train/test split resulted in an overall accuracy of 0.815. In conclusion, CSF cfDNA methylation profiles of diffuse glioma patients exhibit differential methylation patterns between IDH-mutant and IDH-wildtype tumors, as well as between tumor and control, and could be informative biomarkers for the diagnosis of patients with diffuse gliomas.

DISP-09. IMPROVING ADHERENCE TO CANCER CARE IN UNDERSERVED PATIENTS WITH CENTRAL NERVOUS SYSTEM TUMORS

Abstract Patients with central nervous system tumors have disease-specific symptoms such as aphasias, motor symptoms, neuropsychiatric symptoms, or seizures that make treatment adherence difficult. This is further exacerbated by the social determinants of health – patients from historically marginalized groups or those with lower socioeconomic status have additional barriers to treatment. The Integrated Cancer Care Access Network (ICCAN) is a multi-institutional patient navigation program assisting patients who express socioeconomic needs during cancer treatment. In this pilot program, we assessed the impact of ICCAN on treatment adherence and quality of life of CNS cancer patients from marginalized backgrounds. 42 participants with primary brain tumors or brain metastases were recruited from inpatient and outpatient services at Memorial Sloan Kettering Cancer Center to enroll in ICCAN-CNS. Patients were eligible if they were 18 years or older, receiving active treatment or under active surveillance, and screened positive for an essential need. Through standardized patient interviews and questionnaires, we evaluated their needs such as food access, housing, and financial needs. The clinical research coordinator interviewed the patients via phone, taking approximately 60 minutes. The interviews comprised an Essential Needs Assessment, Health Related Social Needs Assessment, NCCN Distress Thermometer, and an ICCAN-CNS questionnaire focused on neurology-specific symptoms. Caregivers helped complete the questions for patients with cognitive impairments. Patients were then matched with resources based on their initial needs assessment. The interviewer conducted 2, 4, and 6-month follow-ups to see if new needs emerged for which resources were provided. Response to the program was overwhelmingly positive with many patients expressing gratitude for the resources provided to them. This pilot demonstrates the feasibility of CNS tumor patients participating in the ICCAN intervention and the need for additional patient navigation programs and interventions that focus on the social determinants of health.

PATH-47. AGE-, SEX-, AND GRADE-ASSOCIATED MOLECULAR DIFFERENCES IN A MULTI-INSTITUTIONAL COHORT OF CHOROID PLEXUS TUMORS

Abstract BACKGROUND Choroid plexus tumors (CPT) are central nervous system tumors where prognosis has been correlated to histologic grade, with aggressive clinical behavior and reduced survival rate in higher grade cases. Here, we present a genomic survey of a large multi-institutional cohort of CPTs across all grades. MATERIAL AND METHODS Fifty-eight CPT samples were analyzed by comprehensive genomic profiling (CGP) by a hybrid capture-based DNA sequencing platform (FoundationOne®CDx). Pathology reports, histopathology reviews, and patient clinical data were assessed. RESULTS Our cohort included 11 choroid plexus papillomas (CPP; grade 1), 16 atypical CPP (grade 2), and 31 choroid plexus carcinomas (CPC; grade 3). Males were slightly more affected than females (31 vs. 27 cases). Median patient age at tissue sampling was 11 years (range: 1–72 years). Median age of patients with CPC was younger at 3 years compared CPP at 34 years (p < 0.01). Genomic analyses identified three frequent, mutually exclusive mutations in TP53, TERTp, and DAXX. TP53 mutations (n = 15, 26%) were significantly more prevalent in CPC (n=14 CPC, p=0.0003), and were identified predominantly in children (n=12 CPC at <20 years). By contrast, TERT promoter mutations (TERTp; n = 5, 8.6%) were identified exclusively in CPP (p=0.019), predominantly grade 2 (4 of 5 cases), and exclusively in adult patients, with a median age of 48 years. DAXX mutations (n=4, 6.9%) were more common in CPC (n=3). Other alterations included PTEN (n=4, all adults) and MYCN amplification (n=3, all children <6 years), both exclusively in CPC. In 21 cases, including 9 out of the 11 Grade 1 CPP, no known cancer mutation was detected. CONCLUSION This study provides comprehensive genomic profiling of CPTs, highlighting distinct genetic alterations associated with different histological grades and patient demographics. These findings may inform future research and therapeutic strategies targeting specific molecular pathways in CPTs.

DISP-03. HEALTH DISPARITIES IN NEURO-ONCOLOGY

Abstract Significant disparities in diagnosis, research, and treatment exist in neuro-oncology. Patients who identify as racial or ethnic minorities, sexual or gender minorities, elderly, rural, or have low socioeconomic status are more likely to have adverse outcomes. Using PubMed and expert opinion, we summarized the existing literature on health disparities in neuro-oncology. We categorized disparities based on primary central nervous system tumors (CNS), secondary CNS tumors, pediatric neuro-oncology, clinical trial enrollment and diversity, and financial toxicity. For patients with primary CNS tumors, we found that marginalized groups faced delays in diagnosis, lower rates of resection, and lower rates of postoperative radiation. For secondary CNS tumors, marginalized groups had lower rates of indicated cancer screening, less access to genetic testing, less access to advanced imaging, and lower rates of stereotactic radiosurgery and targeted therapies. Pediatric neuro-oncology patients had differences in morbidity and mortality based on socioeconomic status and race and faced substantial delays in diagnosis. Financial toxicity, the side effects of the high financial cost of a cancer diagnosis, disproportionately affects marginalized populations. This may be further exacerbated by the use of long-term medications such as IDH inhibitors. There is also unequal representation of diverse populations in neuro-oncology clinical trials. Compared to other cancer subspecialties, there is less available data on disparities, however, the types of disparities such as delays in diagnosis and outcomes are similar. Notably, there are not many interventions focused on mitigating these disparities. There needs to be additional research on health disparities in neuro-oncology, including both descriptions of existing disparities, but also on methods and interventions to address these disparities.

IMMU-60. MYELOID POPULATIONS MODULATE GD2 CAR T CELL ACTIVITY IN DIFFUSE MIDLINE GLIOMA

Abstract H3K27M-mutated diffuse midline gliomas (DMGs) are universally lethal cancers in children and young adults. Our team previously demonstrated efficacy of GD2-targeting chimeric antigen receptor T cells (GD2-CAR T-cells) in preclinical models of DMG of the pons (also called diffuse intrinsic pontine glioma (DIPG) and DMG of the spinal cord, and opened a Phase I clinical trial (NCT04196413) treating patients with first intravenous (IV) followed by repeated infusions of intracerebroventricular (ICV) GD2-CAR T-cells. We employed high-dimensional analyses to define immune states contributing to CAR-T activity in patients. Single cell RNA-sequencing (scRNAseq) was conducted on 555,406 single cells from 115 cerebrospinal fluid (CSF) samples of 13 patients before and after CAR-T treatment. This is the largest CSF CAR-T dataset in central nervous system (CNS) tumors and provides insights into the immune biology surrounding CAR-T treatment for CNS malignancies. Patient CSF samples were dominated by T cell and myeloid populations. After CAR-T infusion, patient CSF exhibited an increased fraction of regulatory T cells and myeloid populations from baseline. Myeloid cells in early timepoints after ICV administration demonstrated a unique pro-inflammatory signature, while CSF samples from IV and late ICV timepoints exhibited a suppressive signature. To further explore the immune biology of these myeloid contributors, we developed a patient-derived xenograft model of DMG relapse following low-dose ICV GD2 CAR-T treatment. Using a pharmacological CSF1R-inhibitor, we demonstrate that depletion of microglia/myeloid cells at a specific window following CAR-T administration enhances durability of tumor control. Together, these data display the power of in-depth correlative analyses to identify distinct immune populations that drive durability of response. Key findings from these data will allow for optimization of CAR-T therapies for H3K27M+ DMG patients, providing hope to shift the paradigm of this fatal disease.

PATH-49. INTRA-OPERATIVE GENETIC ANALYSES FOR DECISION-MAKING DURING TUMOR REMOVAL OF ADULT-TYPE DIFFUSE GLIOMA USING RAPID QUANTITATIVE PCR DEVICE

Abstract BACKGROUND Recent comprehensive molecular analyses of central nervous system (CNS) tumors identified several diagnostic or prognostic markers. Especially, for adult-type diffuse glioma, IDH mutation, TERT promoter (pTERT) mutation and CDKN2A homozygous deletion are quite important markers for diagnosis and prognosis of this type of glioma. Intra-operative identification of these molecular alterations could be effective for decision-making of tumor removal strategy. METHODS In this study, we established intra-operative gene analysis method using rapid quantitative PCR device, GeneSoC, by which we could obtain genotype of these important genes for 20 minutes in an operating room. Using GeneSoC, we could perform 50 cycles of quantitative PCR for approximately 12 minutes. Results; We established rapid gene analyses of mutations of IDH1 R132H, pTERT C225T, pTERT C250T and homozygous deletion of CDKN2A for adult-type diffuse gliomas. For elution of DNA, we incubated at least 1mg of tumor tissue at 95°for 5 minutes. Combined this boiling method with GeneSoC, we could obtain those genetic alterations for 20 minutes after collection of tumor tissue. In analyses of 111 adult-type diffuse glioma cases, sensitivity and specificity for detection of IDH1 p.R132H are 98% and 98%, respectively, and those of pTERT (C225T or C250T) are 100% and 100%, respectively. In analyses of 50 cases, sensitivity and specificity for detection of CDKN2A homozygous deletion are 100% and 83%, respectively. Conclusion; In this study, we could obtain the genotype of important molecular markers intra-operatively, not only during tumor removal but even during tumor biopsy, using GeneSoC device. This rapid genetic analysis might be effective not only for intra-operative diagnosis but also for detection of boundary between tumor and normal tissue.

INNV-08. PRE-CLINICAL AND CLINICAL EVIDENCE FOR THE TREATMENT OF DMG/DIPG USING EMULATE THERAPEUTICS’ ULTRA-LOW RADIO FREQUENCY MAGNETIC FIELD SIGNAL TECHNOLOGY

Abstract EMulate Therapeutics, Inc. (EMTx) has developed a technology that emulates the effects of chemical compounds via a magnetic field. Our research has led to the development of a radio frequency energy (RFE) signal (A1A) that emulates the effects of paclitaxel. Pre-clinical studies demonstrate an effect in slowing down and inhibiting tumor growth. The results of feasibility (Phase I/II) clinical trials testing the EMTx technology for treating recurrent GBM (rGBM) were published in CNS Oncology (CNS Oncol 2023 Pages CNS102, Accession Number: 37462385 DOI: 10.2217/cns-2022-0016). Reported results suggest that the A1A signal is non-inferior to best supportive care (BSC) and when the A1A signal is combined with BSC, a 3-month increase in overall survival (OS) was observed. Diffuse intrinsic pontine gliomas (DIPG) are a rare pediatric central nervous system (CNS) tumor. Survival is measured at under 12 months, with no clinical trials demonstrating a significant increase in OS in 20 years (9 months median survival post radiation therapy). EMTx’s compassionate use program (Hælo® medical device) demonstrated safety and suggested a clinical benefit, with 12 of 14 patients surviving more than 12 months, with median survival of 17 months. EMTx recently completed an orthotopic mouse model of DIPG at University of California San Francisco. The results from exposing the mice to the A1A signal demonstrated a significant survival advantage (P = 0.0163) via the slowing down of cell division. Data to be submitted for peer review publication. The animal model is encouraging and supports the observed results of our compassionate use program. EMTX will submit these results to the FDA for regulatory approval via the Humanitarian Device Exemption pathway. The company will conduct a study with DIPG patients from both the US and India. Subject to FDA protocol approval, 30-35 patients will be recruited to participate in this pediatric neuro-oncology trial, which will be a best supportive care + single therapy (Hælo®) clinical trial.

NCOG-43. THE APPLICATION OF INDUCTION CHEMOTHERAPY COMBINED WITH RADIOTHERAPY IN YOUNG ADULTS WITH CNS GERM CELL TUMORS

Abstract BACKGROUND Central nervous system (CNS) germ cell tumors are rare brain neoplasms, accounting for approximately 0.3-0.5% of all CNS tumors. A combination of radiotherapy and chemotherapy is the standard of care (SOC) in pediatric patients. However, there is no SOC for young adult or adult patients. This study evaluates a regimen of induction chemotherapy followed by radiation in treating young adults with CNS germ cell tumors. METHOD Nine young adult patients diagnosed with pure CNS germinomas were identified in our institution. They underwent a treatment regimen of induction chemotherapies that were planned for four cycles and consisted of bleomycin (three doses per cycle), cisplatin (five doses per cycle) and etoposide (five doses per cycle) followed with whole brain and/or ventricular radiotherapy. The patients’ overall survival (OS), neurological function (including cognition), and adverse events (AE) were analyzed. RESULT Among the nine patients (seven males and two females), the median age is 20 years (range: 17-33 years). They received bleomycin, cisplatin and etoposide (median: two cycles, range: 1-4), and subsequent radiotherapy with plans based on tumor location by radiation oncologists, with a median radiotherapy dose of 45 Gy (range: 36-50.4). Seven patients had a complete response after chemotherapy. The median OS is 53 months (range: 39-121). There is no identifiable cognitive impairment by neurological exam. All patients experienced at least one, reversible, grade 3 AE of myelosuppression. All patients return to their normal baseline including employment. Results of neuropsychological evaluation and all AEs will be presented at the conference. CONCLUSION Induction chemotherapy followed by radiotherapy is potentially safe and effective with manageable and reversible side effects from chemotherapy without cognitive and functional impairment in the nine young adult patients with CNS germ cell tumors. A prospective study of this approach in a clinical trial setting is warranted.

BIOM-02. A HIGH-GRADE GLIOMA, NOT ELSEWHERE CLASSIFIED IN AN OLDER ADULT WITH DISCORDANT GENETIC AND EPIGENETIC ANALYSES

Abstract World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS) uses integrated diagnoses, which incorporates both histologic and molecular features of the neoplasms. With each new iteration, there is refinement and expansion of the diagnostic categories. DNA methylation profiling is a powerful technique to diagnose existing CNS tumors and define new tumor types. However, challenging diagnostic cases that do not conform to the updated WHO classification remain. We present a case of a 72-year-old male with a high grade glioma (HGG) suggestive of high grade astrocytoma with piloid features (HGAP), but it did not “match” to HGAP on DNA methylation profiling, which is essential diagnostic criterion for HGAP. This resulted in an HGG, not elsewhere classified (NEC) diagnosis. This lack of classification posed additional challenges for treatment decision-making.

SURG-02. ANAPLASTIC PLEOMORPHIC XANTHOASTROCYTOMA WITH LEPTOMENINGEAL DISSEMINATION PRESENTING WITH CRANIAL NEUROPATHY IN AN ADULT PATIENT: ILLUSTRATIVE CASE AND REVIEW OF THE LITERATURE

Abstract INTRODUCTION Anaplastic pleomorphic xanthoastrocytomas (APXA) are very rare, grade III malignant astrocytic glial neoplasms first described as a distinct entity in the 2016 World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS). They are generally seen in pediatric and young adult patients as supratentorial lesions with both solid and cystic components and have a high propensity for recurrence despite local treatment. APXAs occasionally demonstrate leptomeningeal dissemination (LMD) but extremely seldom at the time of diagnosis. They are typically treated via surgical resection with adjuvant chemoradiation, although there is no standard of care for adjuvant therapy. Case Presentation: The authors describe the case of a 37-year-old male with a history of seizures since age 11 who presented with four months of worsening headache, increasingly frequent seizures, and diplopia with right cranial nerve III palsy. Imaging at the time of diagnosis of his seizure disorder as a child demonstrated a small left temporal lesion, which remained stable on imaging for over 20 years and was never biopsied, however MRI at current presentation showed significant interval enlargement with intralesional hemorrhage and leptomeningeal enhancement involving the left temporal and parietal lobes, left internal auditory canal, and right oculomotor nerve. He underwent surgical resection with gross total resection achieved and pathology revealed WHO Grade III pleomorphic xanthoastrocytoma with ATG7::RAF1 fusion, 9p21 deletion, and TERT promoter mutation on next generation sequencing. This was followed by adjuvant whole brain radiation with boost and treatment with MEK inhibitor cobimetinib. His postoperative course was remarkable for intermittent speech difficulty and improving right third nerve palsy. CONCLUSION We describe the unusual presentation of an already exceedingly rare primary CNS tumor, namely APXA in an adult patient with LMD and cranial neuropathy at the time of diagnosis, and detail tailored adjuvant therapy based on genomic profiling.

BIOM-42. RESPONSE TO DABRAFENIB/TRAMETINIB IN A PATIENT WITH WHO-CNS GRADE 3 BRAF V600E-MUTATED PLEOMORPHIC XANTHOASTROCYTOMA

Abstract BACKGROUND Pleomorphic xanthoastrocytoma (PXA) is a rare central nervous system tumor. Mutations in BRAF V600E are present in 60-80% of cases. While traditionally managed with surgical resection and adjuvant radiation, emerging evidence suggests targeted therapies may be effective, particularly in cases harboring the BRAF V600E mutation. CASE SUMMARY A 35-year-old male with no significant medical history presented in November 2023 with diplopia and headache leading to the discovery of a large left temporal/parietal tumor. A partial resection was performed. Initial histopathological diagnosis was glioblastoma (GBM); thus, the patient was treated with concurrent radiation and temozolomide for 6 weeks. Molecular pathological analysis demonstrated the presence of BRAF V600E mutation and CDKN2A/B copy number loss. Methylation-based tumor profiling was performed at the National Cancer Institute, with composite methylation profile indicating a consensus match to pleomorphic xanthoastrocytoma. Following chemoradiation, a repeat brain MRI in March 2024 showed tumor progression, prompting the initiation of dabrafenib and trametinib therapy. After 1 month of targeted treatment, a repeat brain MRI demonstrated a partial response with a decrease in tumor size and enhancement. In April 2024, he underwent a planned repeat resection. Symptomatically, the patient experienced intermittent headaches and nausea that were responsive to oral steroids with no serious adverse effects to targeted therapy. DISCUSSION This case highlights the therapeutic potential of double BRAF/MEK blockade with dabrafenib and trametinib in BRAF V600E-mutant anaplastic PXA. The observed partial response on imaging suggests the efficacy of targeted therapy in this molecular subtype. These findings underscore the importance of molecular profiling in guiding treatment decisions.

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-37. A NEW SUBTYPE OF DIFFUSE MIDLINE GLIOMA, H3 K27 AND BRAF/FGFR1 CO-ALTERED, EXHIBITS SPECIFIC BIOLOGICAL CHARACTERISTICS AND NEW THERAPEUTIC VULNERABILITIES

Abstract Diffuse midline gliomas (DMG) H3 K27-altered are incurable grade 4 gliomas and represent a major challenge in neuro-oncology. This tumor type is classified in four subtypes by the 2021 edition of the WHO Classification of the Central Nervous System tumors. However, we recently identified a new subtype of DMG by assembling a retrospective cohort of 60 adult and pediatric DMG cases harboring BRAF or FGFR1 mutations in addition to the H3K27M mutation or EZHIP overexpression. Comprehensive clinical, histological, radiological, and genomic, analyses allowed to identify distinct genotype-phenotype characteristics. Contrary to other DMG, these tumors occur more frequently in the thalamus (27% vs. 70% for BRAFV600E or 58% for FGFR1MUT), and in adults in the case of FGFRMUT tumors. Importantly, these patients display a longer overall survival with a median above three years. Unsupervised analysis of DNA methylation profiles regrouped these MAPK-altered DMG in a methylation cluster distinct from other DMG H3K27, but also lower-grade midline tumors driven by FGFR1 or BRAF mutations Additionally, this new DMG subtype harbors atypical radiological and histopathological profiles with calcification and/or a solid tumor component both for BRAFV600E and FGFR1MUT cases that can suggest this differential diagnosis. Further analyses of the transcriptome of these tumors compared to canonical DMG H3K27-altered showed an expression signature of senescence with activation of a TP53/CDKN1A axis, together with a strong upregulation of the PI3K/AKT/MTOR pathway. Our current modelling of the drug response using patient-derived models of these specific DMG will permit to rapidly prioritize treatment strategies. Additionally, our clinical experience in treating these patients suggests a higher response to everolimus and imipridone ONC201 in this specific subtype. In conclusion, DMG H3 K27 and BRAF/FGFR1 co-altered, represent a new subtype of DMG with distinct specific characteristics compared to canonical DMG H3K27 and data accumulated strongly support their separate stratification in clinical trials and specific therapeutic managements.

PATH-05. CLINICAL, PATHOLOGICAL AND MOLECULAR DISEASE CHARACTERISTICS OF DIFFUSE HEMISPHERIC GLIOMA, H3 G34-MUTANT

Abstract BACKGROUND Diffuse hemispheric glioma, histone 3 (H3) G34-mutant, is a pediatric-type diffuse high-grade glioma newly defined in the World Health Organization (WHO) classification of central nervous system tumors 2021. Here we sought to define the prognostic roles of clinical, neuroimaging, pathological, and molecular features of these tumors. METHODS We retrospectively assembled a cohort of 114 patients with diffuse hemispheric glioma, H3 G34-mutant and profiled the imaging presentation and the molecular landscape of their tumors. RESULTS Compared with glioblastoma, H3 G34-mutant tumors exhibited less avid contrast enhancement, less necrosis and less edema on MRI. Comprehensive analyses of mutational and DNA copy number profiles revealed recurrent mutations in TP53 and ATRX, homozygous deletions of CDKN2A/B, and amplifications of PDGFRA, EGFR, CCND2, and MYCN. MGMT promoter methylation was detected in 79 tumors (75%); 11 tumors (13%) showed DNA copy number profiles suggestive of circumscribed deletions on 10q26.3 involving the MGMT locus. Median survival was 21.5 months (95% CI 15.3-27.7) and eight patients (7.0%) survived for ≥ five years. Female sex, gross total resection, and MGMT promoter methylation were positive prognostic factors on univariate analysis. Among radiological, pathological and molecular features, absence of pial invasion, and presence of microvascular proliferation and CDK6 amplification were positive prognostic factors on univariate analyses. CONCLUSION This study refines the clinical and molecular landscape of H3 G34-mutant diffuse hemispheric gliomas. Dedicated trials for this novel tumor type are urgently needed.

EXTH-37. ALLOSTERIC MITOCHONDRIAL CLPP AGONIST ONC206 ALTERS STRESS RESPONSE, METABOLIC AND EPIGENETIC PROFILES TO ELICIT ANTI-CANCER EFFICACY IN HIGH-GRADE GLIOMAS

Abstract Dordaviprone (ONC201) is a dopamine receptor D2/3 (DRD2/3) antagonist and allosteric ClpP agonist that has demonstrated durable responses in recurrent H3 K27M-mutant glioma patients. ONC206, a derivative of ONC201 with nanomolar potency that also targets DRD2/3 and ClpP, is in Phase I trials for central nervous system tumors. We characterized target relevance, human ClpP binding, in vitro efficacy, downstream signaling and response determinants associated with ONC206 in high-grade gliomas (HGG). Co-crystallization with ClpP that assembles as a tetradecameric complex revealed an allosteric ligand interaction with distinctions in the ONC206-ClpP overall conformation relative to the ONC201-bound or apo complex, including an increase in the resolved pore size and decreased complex height. ONC206 was more potent than ONC201 in cell-free human ClpP casein/peptide degradation assays). Accordingly, HGG cell lines and patient-derived cells exhibited increased sensitivity to ONC206 relative to ONC201 and generally required a shorter duration of exposure. Unlike DRD2, CRISPR-mediated ClpP knockout in HGG cell lines blunted ONC206 sensitivity. Metabolomics revealed elevated α-ketoglutaric acid, α-hydroxyglutaric acid, and glutaric acid. Proteomics indicated inhibition of multiple mitochondrial pathways including OXPHOS and TCA cycle. TCA cycle enzyme α-ketoglutarate dehydrogenase (KGDH) was inhibited in a ClpP-dependent manner. Western blotting showed downregulated ClpX, and upregulated ATF4/CHOP, H3 K27me3 and H3 K36me3. Next-generation sequencing of acquired resistance cell lines, which exhibited cross-resistance to ONC201 and ONC206, revealed diverse ClpP missense mutations distributed across various monomer interfaces. Both intrinsic and well as ONC206-stimulated ClpP proteolysis were mitigated by these mutations, which was congruent with an absence of the tetradecameric assembly. These ClpP mutations recapitulated resistance and, conversely, wildtype ClpP overexpression restored sensitivity. Thus, allosteric ClpP agonism is a key determinant of ONC206 activity in HGG by altering stress response, metabolic, and epigenetic profiles.

CNSC-34. SURGICAL INTERVENTION ASSOCIATION WITH THE DEVELOPMENT OF SUBSEQUENT DISSEMINATION IN CHILDHOOD DIFFUSE INTRINSIC PONTINE GLIOMAS (DIPG)

Abstract BACKGROUND Diffuse intrinsic pontine glioma (DIPG) is one of the most aggressive pediatric central nervous system tumors, and currently, there are no curative treatment options available. With the increasing application of molecular diagnostics, more and more DIPG patients are recommended to undergo surgery; however, its correlation with dissemination needs to be better understood. Hence, we conducted this cohort to analyze the predictors of subsequent metastasis in pediatric DIPGs. METHODS The final analysis included 142 pediatric (age ≤ 12) DIPG patients treated at Sanjiu Brain Hospital between January 2017 and September 2023. The data were retrospectively collected following the initial diagnosis. Patients were followed up for 6 months. The primary endpoint was the occurrence of subsequent metastasis. Univariable and multivariable logistic regression analyses were utilized to identify statistically significant predictors of subsequent dissemination. All statistical assessments were two-tailed, and only P < 0.05 was deemed to be statistically significant. RESULTS Among 142 patients, 14(9.9%) developed metastasis within the follow-up time. There were 77(54.2%) males and 65(45.8%) females. The median age was 7 years (ranging 1 - 12 years). The overall cohort demonstrated that surgery was the only predictor of dissemination both in univariable (OR 4.567, 95%CI 1.351 – 20.901, P = 0.024) and multivariable (OR 5.501, 95%CI 1.560 – 26.105, P = 0.014) analyses. However, subgroup analysis involving patients who received surgical intervention showed that biopsy was not superior nor inferior to resection in terms of relative risk for subsequent dissemination (16.7% vs. 15.8%). CONCLUSION Surgical intervention increases the relative risk of dissemination occurrence to four times more than those who did not receive surgery. Surgical intervention is crucial given the potential of molecular analysis leading to improved therapeutic options. Nonetheless, patients should be informed about the risks associated with surgery, including subsequent metastasis.

TMOD-07. DEVELOPMENT AND CHARACTERIZATION OF A SPINAL CORD DIFFUSE MIDLINE GLIOMA MODEL

Abstract Diffuse midline gliomas (DMGs) are very aggressive central nervous system tumors that occur mainly in children and adolescents. Most DMGs develop in the brainstem, but they can also be found in the thalamus and the spinal cord, the latter comprising 4% of all DMGs. Despite advances in current treatments, the outcome for DMG patients remains extremely poor. The success of immunotherapy in other tumors encourages its translation to DMGs, for which the understanding of the tumor immune microenvironment (TIME) is imperative. The field counts with several murine DMG models in the pontine and thalamic locations. However, there is a paucity of spinal cord models. Thus, in this work, we have generated an orthotopic syngeneic model of H3K27M spinal cord DMG by injecting the tumor cells directly into the spinal cord under the T2 vertebra. We monitored tumor growth by bioluminescence and PET using 18F-FDG and 11C-methionine. As the tumor grew, we observed human-like symptoms in the mice, such as hemiplegia and hemiparesis. TIME characterization showed that this tumor model is mainly infiltrated by macrophages and almost devoid of lymphocytes. We are currently delving into the phenotype of these populations by scRNAseq and spatial transcriptomics. In addition, we are comparing our findings with human samples (n=15) to assess whether our model mimics human disease and can serve as a bonafide model of this tumor location. As a proof of concept, treatment of spinal DMG-bearing mice with a TIM-3 antagonist antibody, previously described as effective in pontine DMG-bearing mice, increased the median overall survival. We showed by microPET imaging that anti-TIM-3 administration into the brain ventricles diffuses to the tumor. These results open a path for the characterization of the spinal cord DMG TIME and for testing preclinical treatments in this new model.

EPCO-05. GENOMIC AND CLINICAL INSIGHTS FROM A LARGE-SCALE STUDY OF 172 RETINOBLASTOMAS

Abstract Retinoblastoma, a pediatric ocular cancer, is the only central nervous system tumor visible without specialized tools, readily detectable with the naked eye. This rare childhood cancer is mainly driven by mutations in RB1 or MYCN amplification, posing significant challenges in pediatric oncology. We conducted whole exome sequencing on 172 retinoblastoma tumors along with matched blood DNA from 171 patients, which included 119 unilateral, 49 bilateral, and three trilateral cases. Our analysis identified pathogenic variants in RB1 in 76 patients and MYCN duplication in 79 cases, highlighting their crucial roles in the disease. Additionally, we found mutations in RPTOR and TSC2, components of the mTOR signaling pathway, in two patients. Notably, our copy number alteration analysis revealed recurrent arm-level changes, including gains on 1q (23.3%), 2p (20.9%), and especially 6p (41.3%), along with other changes such as 5p gain (8.1%), 17q gain (8.1%), and 16q loss (5.8%). Our findings link these genetic alterations to specific clinical features; for instance, 6p gains were associated with Rubeosis, subretinal seeds, and tumor LC beyond, while 17q gains were linked to Rubeosis. Furthermore, gene collapsing techniques identified MATR3 and CYP4F2 as additional novel retinoblastoma-related genes, and module identification analysis pinpointed retinoblastoma-associated modules including HLA-DRB1-CBL, LPAR2, RB1, and TRIM28. Our study, the largest cohort of its kind, underscores the importance of next-generation sequencing from understudied populations in uncovering the complex genetic landscape of retinoblastoma, emphasizing the potential of precision medicine to enhance therapeutic strategies and improve outcomes for retinoblastoma patients.

NCOG-33. MTOR INHIBITORS AS ADJUVANT TARGETED THERAPY IN PEDIATRIC PATIENTS WITH PROGRESSIVE OR REFRACTORY LOW-GRADE GLIOMA: A SINGLE-CENTER RETROSPECTIVE STUDY

Abstract Low grade gliomas (LGG) represent about one-third of all pediatric central nervous system tumors, with about half having disease progression despite upfront surgery and adjuvant therapies. Current treatments for LGG progression either produce toxic side effects (i.e., radiation therapy) or do not generate durable responses. Targeted agents are an effective way of attacking tumors with identified genetic mutations, but in some cases, a complete response can be subverted by the heterogeneity of tumors. Additionally, most tumors do not carry any targetable mutations. Temsirolimus and everolimus are mTOR inhibitors that have previously been shown to be well-tolerated in early clinical studies in pediatric solid tumors. We performed a retrospective study to look at the toxicity profile of mTOR inhibitors when given in combination therapy and treatment response in patients with progressive or refractory LGG. We examined 20 patients with a diagnosis of LGG including mixed glioma and glioneuronal tumors who received treatment at our institution from 2016-2024 with targeted therapy, of which 8 patients also received temsirolimus or everolimus. Of these 8 patients, 2 had partial response, 2 had minor response, 3 had stable disease, and 1 had progressive disease. The average number of cycles received was 13.6 (range 3-24). Most observed side effects were grade 2 or less, including nausea, transaminitis, myelosuppression, diarrhea, and hyperlipidemia while grade 3/4 toxicities that required dose modification included mucositis, hyperglycemia, and hyperlipidemia. Overall, the addition of temsirolimus to treatment regimens of pediatric patients with heavily pretreated refractory LGG prolonged progression free survival by an average of 478 days with only one patient progressing while on therapy. These results demonstrate feasibility and preliminary efficacy of adding mTOR inhibitors as adjuvant therapy in this patient population. There is dire need of large prospective collaborative studies in the future.