Pediatric CNS Tumors Research Articles

BIOM-20. EVALUATING THE POTENTIAL OF PSMA TARGETING IN CNS TUMORS: INSIGHTS FROM LARGE-SCALE TRANSCRIPTOME PROFILING

Abstract PURPOSE Prostate-specific membrane antigen (PSMA) is a well-established target in prostate cancer therapy that has shown potential as a theranostic target across non-central nervous system (CNS) and CNS tumor types. We aimed to investigate the pan-tissue expression pattern of the PSMA-encoding gene FOLH1 to assess whether transcriptome profiling can inform tumor theranostics. EXPERIMENTAL DESIGN We assessed FOLH1 expression from the Open Pediatric Cancer Project (OpenPedCan, n = 2132 specimens), The Cancer Genome Atlas (TCGA, n = 10411 specimens), and the Genotype Tissue Expression Project (GTEx, n = 17382 specimens) in relation to published reports of PSMA radionuclide uptake. RESULTS When comparing FOLH1 expression across tumor versus normal tissues, we found that non-CNS tumors exhibiting elevated expression of at least two-fold (FDR < 0.05) were reported to have successful PSMA radionuclide uptake in contrast to tumors with less than a two-fold elevation or with lower expression of FOLH1 relative to normal. Notably, CNS tumors universally exhibited lower expression of FOLH1 relative to normal brain tissue, but we observed considerable variation in the expression of blood-tumor barrier (BTB) components associated with reports of BTB integrity and uptake of PSMA radiotracers. CONCLUSIONS Large-scale transcriptomics data may help guide the application of PSMA-based radionuclide therapies in non-CNS tumors, but care should be taken to account for BTB effects in CNS tumors when assessing the potential for radionuclide success. Our analysis demonstrated that FOLH1 showed a lack of tumor-specific expression for both adult and pediatric CNS tumors when compared to normal brain tissue, suggesting that PSMA is not a desirable target in this disease type. This study highlights the utility of utilizing large-scale molecular data to guide the selection of theranostic targets.

Individual- and community-level correlates of pediatric central nervous system tumor disparities in the US.

The aim of this study was, through comprehensive, multilevel models of social determinants of health (SDoH) factors, including the Yost Index socioeconomic status (SES) score, to determine whether community- or individual-level SDoH factors quantifiably influence pediatric CNS tumor disparities more in care and prognosis across the US. The authors performed a retrospective cohort study assessing specialized Surveillance, Epidemiology, and End Results data of pediatric patients (≤ 19 years old) with nonmalignant and malignant tumors of the CNS from 2010 to 2018. A census-level Yost Index SES score and rurality/urbanicity measures were incorporated with individual characteristics of age, sex, and race/ethnicity. Chi-square analyses for clinical and demographic descriptions, multivariate Cox proportional hazards logistic regressions for survival, and multivariate logistic regressions for resection, radiation treatment, treatment delay, and advanced staging on preliminary presentation were performed. Across 18,236 patients, age-adjusted analyses showed substantially increased mortality risk among 6 of 11 subtypes (highest hazard ratio [HR] 1.91, 95% CI 1.59-2.28, p < 0.001 for glioma NOS), decreased odds of first-line therapy among 7 of 18 subtypes (lowest OR 0.36, 95% CI 0.11-0.97, p = 0.043 for resection of choroid plexus papilloma), increased odds of treatment delay among 6 of 11 subtypes (highest OR 2.47, 95% CI 1.01-6.49, p = 0.047 for germinoma), increased odds of advanced staging on preliminary presentation among 3 of 10 malignant subtypes (highest OR 2.56, 95% CI 1.27-5.52, p = 0.008 for malignant ependymomas), and increased odds of receipt of radiation therapy among 3 of 10 malignant subtypes (highest OR 2.30, 95% CI 1.87-2.84, p < 0.001) observed across many disease subtypes contributed by certain individual- and community-level SDoH factors. Through comprehensive analyses combining individual- and community-level SDoH factors, this study identified detrimental interrelated SDoH associations with poorer care and prognosis of pediatric patients with CNS tumors, delineating how both levels differentially contribute to observed disparities across different subtypes.

Central nervous system pediatric multi-disciplinary tumor board: a single center experience

BackgroundThe Multidisciplinary Tumor Board (MTB) is a collaborative platform involving specialists in oncology, surgery, radiology, pathology, and radiotherapy, and aims to optimize diagnostics and treatments. Despite MTB’s widespread benefits, limited literature addresses its application in pediatric neuro-oncology. After a literature revision on pediatric neuro-oncology MTB, our study describes our institute’s pediatric neuro-oncology MTB, focuses on evaluating its impact and the neuroradiologist’s role in patient-centric approaches, considering recent genetic insights into pediatric brain tumors.Materials and methodsLiterature Review concerning pediatric neuro-oncology MTB from January 2002 to June 2024. Clinical Data: retrospective study of all patient files presented in the pediatric neuro-oncology MTB (pnMTB) between 2019 and 2022. Statistical analysis was mainly carried out by directly comparing the absolute or relative values of the respective parameters examined; qualitative variables compared mainly with the chi-square test, quantitative variables mainly with the t-test.ResultsLiterature Review: 7 papers encompass a multidisciplinary approach for the pediatric CNS tumors.Clinical dataA total of 236 discussions were analyzed representing 107 patients. Median age was 14,3 years (range: 6 months – 17 years). The requests for case evaluations primarily came from the pediatric oncologists (83%) and neurosurgeons (14.8%), and they were mainly addressed to the neuroradiologists (70.3%). Proposals during pnMTB mainly involved imaging follow-up (47.8%) and management with chemotherapy (34.7%). Changes in patient treatment (CPT) occurred in 115 cases, and pediatric neuroradiologist intervention contributed to 72.4% of these changes.ConclusionThanks to their multidisciplinarity, high number of cases discussed, and usual respect for their proposals, the pnMTB has made it possible to improve the coordination among specialties involved in patient management, to apply the recent protocols, and to exchange knowledge among teams managing pediatric CNS tumors.

555: Re-irradiation in paediatric CNS-tumours: Outcome after implementing national guidelines

555: Re-irradiation in paediatric CNS-tumours: Outcome after implementing national guidelines

2405: Voxel-based analysis of cognitive outcomes after radiotherapy for paediatric CNS tumours

2405: Voxel-based analysis of cognitive outcomes after radiotherapy for paediatric CNS tumours

2674: Local reirradiation of pediatric CNS tumors with proximity to brainstem using proton beam therapy

2674: Local reirradiation of pediatric CNS tumors with proximity to brainstem using proton beam therapy

IMG-05. USING CONVOLUTIONAL NEURAL NETWORKS TO IDENTIFY COMMON MOLECULAR ALTERATIONS IN PEDIATRIC BRAIN TUMORS

Abstract BACKGROUND Artificial intelligence (AI) and deep learning have had increased uses in healthcare. Initial studies have shown it is possible to predict multiple tumor types in adults and children using convolutional neural networks (CNN), a form of deep learning, using MRIs. In pediatric CNS tumors, molecular alterations are used in both diagnosis and treatment decisions. This project aims to verify that we can use deep learning to help diagnose and molecularly classify primary pediatric CNS tumors. Previously, we used Recurrent Health’s platform to predict high vs. low grade CNS lesions to &amp;gt;95% recall and 85% precision in pediatric patients. The objective of this study is to validate the AI’s ability to predict common genetic alterations with 90% accuracy. METHODS This retrospective study evaluated patients (ages 0-21) with histologically confirmed primary CNS tumors that underwent BRAF molecular analysis. We collected demographic data: age, tumor location, and presence of BRAF mutations/fusions. The data was divided into a training and validation set (80%/20% split). To determine the viability of models, we will measure specificity, sensitivity, and F1 Score (Sorenson-Dice coefficient) for predicting genetic alterations. Model score confidence was achieved through K-fold cross-validation and statistical power analysis with a finite population coefficient to determine the appropriate sample size. RESULTS Our retrospective test included 136 patients with multiple scans for training, model validation and testing. The CNN was able to predict presence of BRAF fusions with &amp;gt;95% recall/sensitivity, &amp;gt;76% precision/specificity and F1/accuracy &amp;gt;87% while predicting BRAFV600 mutations with &amp;gt;75% recall/sensitivity, &amp;gt;95% precision/specificity and F1/accuracy &amp;gt;85%. These metrics indicate strong discrimination in classification. CONCLUSIONS Preliminary data suggests the accuracy of the model in identifying the presence of BRAF mutations, providing a potential opportunity for a non-invasive tool to help aid in diagnosis and help guide initiation of targeted therapy.

OTHR-29. A SINGLE INSTITUTION REVIEW REGARDING TRENDS IN THE MOLECULAR ANALYSIS OF PEDIATRIC CENTRAL NERVOUS SYSTEM (CNS) TUMORS AND GERMLINE ANALYSIS BETWEEN 2019 – 2023, EMPHASIZING THE IMPORTANCE OF EASY ACCESS TO COMPREHENSIVE TESTING

Abstract BACKGROUND Molecular characterization of pediatric CNS tumors improves diagnostic accuracy and guides treatment. Germline analysis is also important to uncover cancer predisposition syndromes, which influence the approach to treatment and tumor surveillance. The options for molecular assessment are influenced by availability, including access through a trial or insurance approval. METHODS A retrospective review of the molecular workup performed on all CNS tumors biopsied/resected at Children’s Minnesota from 2019 – 2023 was undertaken to look at trends in the specific tests performed over time and how the molecular results guided treatment. RESULTS Between 2019 – 2023, 220 patients at Children’s Minnesota were diagnosed with a CNS tumor. A total of 191 underwent surgery and 162 (85%) had sufficient tissue for molecular analysis. There was no apparent difference in the percentage of patients who underwent IHC/FISH/NGS between 2019 - 2023, but methylation profiling frequency increased over time (2019 2%, 2020 and 2021 10%, 2022 58% and 2023 71%). Frequency of germline analysis also increased (2019-2021 29%, 2022-52% and 2023-63%). Easy availability of comprehensive molecular and germline analysis for patients enrolled on COG-APEC14B1 is credited for these improving trends. Molecular analysis confirmed (59%) or supported (36%) the diagnosis, and guided treatment in 30% of cases (stratification of treatment in 89% of medulloblastoma and targeted treatment in 63% of high-grade glioma, 9% of medulloblastoma and 6% of low-grade glioma). Methylation profiling alone accurately diagnosed 79% of cases, including subtyping tumors. Germline analysis detected a pathogenic germline alteration in 14% of CNS tumor patients (NF1 5%; TP53 and BRIP1 1%; PALB1, NF2, TS2, SMARCB1, biallelic PMS2, CHEK2, FANCA, ORICH1 and SDHA 0.5%). CONCLUSION These findings demonstrate the importance of easy access to comprehensive molecular and germline analysis with quick turnaround time to provide the best diagnosis, prognosis and treatment options for pediatric CNS tumor patients.

DIPG-88. TARGETING THE ANTIOXIDANT RESPONSE ELEMENT AXIS SENSITIZES DIFFUSE MIDLINE GLIOMA CELLS TO ONC201

Abstract BACKGROUND Diffuse midline glioma (DMG) is a universally fatal CNS tumor, with a median overall survival of &amp;lt;12-months. Recent studies, including our own, have identified overexpression of the mitochondrial protease ClpP in DMG patient samples. ClpP plays a pivotal role in regulating energy production. Brain-penetrant ClpP agonists, including ONC201, ONC206, and TR107, induce non-specific degradation of the mitochondrial electron transport chain. However, there is considerable variability in the response of DMG cell lines to these therapies, with only about half reaching IC50. Notably, TP53-mutant cell lines exhibit reduced sensitivity. METHODS/RESULTS Further analysis using quantitative proteomics of TP53-mutant DMG cell lines exhibited hallmark activation of ClpP, increased mitochondrial stress and dysfunction. Importantly, ClpP agonism increased the activity of the transcription factor NRF2, driving expression of NQO1 (p=0.0017). NQO1 is a cytoprotective enzyme, promoting redox balance and cell survival. This highlights a potential adaptive response to ClpP agonist therapy in DMG cells. Analysis of DMG patient samples through publicly available RNA sequencing data identified ubiquitously high NRF2 expression compared to other pediatric CNS tumors. This led us to hypothesize that a clinically relevant, selective NQO1 inhibitor could elicit a strong response to ClpP agonism. Therefore, we examined ARQ761, a CNS-active therapy that disrupts NQO1 leading to the formation of an unstable hydroquinone, causing oxidative DNA damage and apoptosis. When ARQ761 was used concurrently with a ClpP agonist, the combination showed additive effects, average Bliss Score of 9.91 (n=4). Interestingly, administering ARQ761 24 h after ClpP agonist exposure combined synergistically, average Bliss Score of 15.87 (n=4). This synergy was further potentiated using ARQ761 48 h after ClpP agonism, when NQO1 expression peaked, resulting in an average Bliss Score of 20.30 (n=4). CONCLUSIONS This study has unveiled an intrinsic antioxidant defense mechanism in DMG, which facilitates evasion from treatments inducing oxidative stress. This defense mechanism appears particularly robust in cell lines harboring TP53-mutations, which are also known to exhibit resistance to radiotherapy.

ETMR-07. OVEREXPRESSION OF THE PLAG-GENE FAMILY MEMBER PLAG1 DURING MURINE BRAIN DEVELOPMENT LEADS TO ABERRANT EXPRESSION OF IMPRINTED GENES AND THE FORMATION OF MIDLINE BRAIN TUMORS

Abstract BACKGROUND The transcription factor PLAG1, ordinarily active during development, has been identified as overexpressed in several pediatric brain tumor entities, including H3 K27-altered diffuse midline glioma. Additionally, our group recently identified a novel type of embryonic CNS tumors with amplification of the related genes PLAGL1 and PLAGL2. How this aberrant PLAG family gene activation drives tumor formation is unknown. We hypothesize that aberrant activity of these transcription factors impedes normal differentiation, thereby fostering neoplastic transformation. METHODS To investigate this, we utilize transgenic mouse models engineered to exhibit targeted PLAG1 overexpression and loss of Trp53 during brain development. Following, we use bulk and single-cell RNA-seq to examine underlying mechanisms and are working on whole genome CRISPR-Cas9 screens to detect genetic dependencies in derived tumorsphere cultures. RESULTS We found that transgenic mice develop brain tumors in the midline. RNA-seq of these tumors suggests the activation of developmental (homeobox transcription factors) and imprinted genes e.g. H19 and Dlk1, the latter being similarly activated in pediatric CNS tumors with PLAGL1/2 amplification. Using single-cell RNA-seq of the resultant tumors, we compared the gene expression profiles of the tumor cells to a developmental mouse brain atlas. Tumor cells best correlated to radial glia stem cells and glioblasts, supporting the hypothesis of a developmental block caused by PLAG1 overexpression. A subpopulation of the tumor cells seemed to escape the radial glia cell state but were then ultimately locked in the OPC state. A similar mechanism was observed in H3 K27M diffuse midline gliomas. CONCLUSION Collectively, we provide evidence that PLAG1 overexpression drives pediatric brain tumor formation by inhibiting normal cellular differentiation. The ongoing CRISPR screen in PLAG1 and PLAGL1 overexpressing murine cell lines, ChIP-seq analysis of the murine tumors, and comparisons with human data and hNSC models aims to unveil the specific molecular mechanisms underlying tumor progression.

SURG-04. COMPARABLE SAFETY OF INTRATHECAL CHEMOTHERAPY GIVEN VIA LUMBAR PUNCTURE OR INTRAVENTRICULAR RESERVOIRS FOR PEDIATRIC CENTRAL NERVOUS SYSTEM (CNS) TUMORS: A SINGLE-INSTITUTION EXPERIENCE

Abstract BACKGROUND Intrathecal (IT) delivery of chemotherapy is utilized for the treatment of pediatric cancers, particularly leukemia and CNS tumors, either via lumbar puncture (LP) or intraventricular reservoir (IR). While the latter allows easier administration and more frequent IT dosing, data are lacking on the comparative safety and efficacy between these administration routes. We now present the IT chemotherapy experience from a single high-volume pediatric neuro-oncology center. METHODS We performed a retrospective chart review of patients with primary CNS tumors treated with IT chemotherapy between the years 2004-2022 at Dana-Farber/Boston Children’s Hospital. We collected demographic, clinical and outcome data. Safety evaluation included review of immediate (procedural) and short-term post-procedural assessments. RESULTS We identified 74 patients who received a total of 1,211 IT chemotherapy administrations. Excluding patients with insufficient data, we report on 38 patients who received 717 administrations (LP, n=207; IR, n=510). Median age was 26.5 months (range, 0.1-14.5), and diagnoses included medulloblastoma (n=14), ATRT (n=14) and others (n=10). Immediate events were reported in 11 (0.2%) IR and 1 (0.4%) LP administrations, i.e technical (n=5), high ICP (n=3), and immediate adverse side effects (n=3). Short-term events were reported in 16 (3%) IR and 12 (5.8%) LP administrations, i.e. fever (n=6), seizures (n=6), arachnoiditis (n=4), and others (n=10). No grade 4-5 adverse events were reported. No statistically significant difference was found between routes of administration and the rate of immediate or short-term events. Of note, 14/18 (78%) patients with CSF-positive disease achieved CSF clearance, with median time to response of 57 days (range, 27-446). CONCLUSIONS IT chemotherapy shows an excellent safety profile in children with malignant CNS tumors, with no differences between IR and LP administration. IT delivery can be efficacious in CFS clearance for patients with metastatic disease, lending support to inclusion of IT chemotherapy in current treatment regimens.

NURS-21. EXPLORATION OF CORRELATIVE STUDIES IN EARLY PHASE TRIALS FOR PEDIATRIC AND YOUNG ADULT CENTRAL NERVOUS SYSTEM (CNS) TUMORS AND THE POTENTIAL TRANSLATION TO CLINICAL CARE

Abstract BACKGROUND Correlative studies are common in early phase clinical trials. In addition to primary aims establishing maximum tolerated dose or efficacy, supplementary information from biospecimens is frequently collected with patient consent. The Pediatric Neuro-Oncology Consortium (PNOC) has included several correlative studies with implications for understanding patterns in the development of tumors, response to treatment, and prognosis. A needs assessment survey of PNOC institutions by the Advanced Practice Provider and Investigational Nurse Committee (APPNIC) highlighted that nurses and advanced practice providers (APPs) desire further education regarding correlative studies. METHODS Blood, stool, cerebrospinal fluid (CSF) and hair strands are examples of correlative biospecimens incorporated in PNOC protocols. We will share a review of the literature and implications for practice. RESULTS Blood, drawn in conjunction with clinical labs, is commonly analyzed for circulating tumor DNA to conduct molecular profiling in blood compared to tissue, explore less invasive means of molecular evolution of tumor somatic mutations, and identify early markers of tumor response or resistance. Stool is collected to utilize the gut microbiome as a lens into treatment response in CNS tumors via the gut-brain axis. Stool samples are compared to normal controls and longitudinally within patients during treatment. CSF sampling provides less invasive disease monitoring, tumor molecular characterization, markers of tumor response or resistance, and drug pharmacokinetics. Hair sampling can be used to further quantify drug levels for pharmacokinetics and assess treatment compliance. The robustness of these correlative samples collected at various timepoints (diagnosis, pre-surgery and post-surgery, post-radiation and/or with recurrence) informs on prognosis, response to treatment; and ultimately, interventions to improve outcomes for pediatric and young adult CNS tumors. CONCLUSION Our assessment identified a need for APP and nursing-focused education on biospecimen collection to inform on emerging clinical and research advances while improving protocol compliance.

BIOM-14. UTILITY OF MIRNA-BASED LIQUID BIOPSY AND RADIOGRAPHIC IMAGING IN PEDIATRIC BRAIN TUMOR PATIENTS

Abstract BACKGROUND MRI is the current gold standard imaging technique for diagnostic evaluation and monitoring of pediatric CNS tumors; however, MRI measures can only provide inference into tumor biology and molecular stratification. miRNAs are an abundant and stable nucleic acid found circulating in blood and cerebrospinal fluid (CSF) and can be utilized as a tumor biomarker. METHODS We hypothesized that correlating miRNA biomarkers with radiological tumor measurements may provide improved diagnostic and monitoring for patients with pediatric brain tumors. Using a cohort of 54 pediatric brain tumors including low grade glioma, ependymoma, germ cell tumor, medulloblastoma, atypical teratoid rhabdoid tumor and high-grade glioma we attempted to combine MRI findings and circulating miRNA data. The miRNA expression was profiled in 33 CSF and 52 plasma samples using the HTG EdgeSeq platform. Clinically acquired, multi-parametric MRI scans at time-points close to liquid biopsy collection were collected retrospectively and used to generate volumetric tumor segmentations. Machine learning methods were implemented to evaluate combinatory features. RESULTS We identified unique miRNA targets that significantly correlated with MRI features, clinical findings, and patient outcomes. In both CSF and plasma, miRNA expression was found to correlate with diagnosis and clinical features including tumor grade and disease burden (p &amp;lt; 0.05). In CSF, miRNA expression was correlated with MRI features including cystic core presence, edema, leptomeningeal disease and tumor location (p &amp;lt;0.05). In plasma, differences in miRNA expression were related to MRI measurements including cystic core volume, location, and leptomeningeal disease (p &amp;lt; 0.05). Combination of miRNA targets for plasma or CSF with imaging-based features significantly improved histology specific multimodal diagnosis predictions. CONCLUSIONS These results demonstrate the potential utility of miRNAs as a pediatric brain tumor biomarker which when combined with imaging features can improve minimally and non-invasive diagnostics and the subsequent management of pediatric brain tumor patients.

GCT-18. GERMINOMAS OF THE CENTRAL NERVOUS SYSTEM (CNS): 20 YEARS EXPERIENCE WITH WHOLE VENTRICULAR IRRADIATION (WVI) AT FONDAZIONE IRCCS ISTITUTO NAZIONALE DEI TUMORI, MILAN

Abstract BACKGROUND Intracranial germ cell tumors account for 1-3% of pediatric CNS tumors, with germinomas constituting up to 65%, their prognosis being favourable compared to the non-germinomatous counterpart. METHODS After an unsuccessful experience with focal irradiation, from 2001 to 2021 we treated 68 patients (51 males/17 females, median age at diagnosis 16 years) with 4 PEB cycles (cisplatin 25 mg/sqm days 1-4, etoposide125 mg/sqm days 1-4, bleomycin 18 mg/sqm day 2, cycles every 21 days) followed by whole ventricular irradiation (WVI) 30,6 Gy/36Gy if CR/PR-SD. Patients with metastatic disease received craniospinal irradiation only (CSI 24 Gy+16Gy TB-tumor bed/WVI). RESULTS Fifty-nine patients had localized disease: 23 pineal, 22 suprasellar, 13 bifocal, 1 in the basal ganglia and 9 were metastatic. Suprasellar localization was associated with longer diagnostic delay. Five, 10 and 20 years OS and EFS were 100%, 97.5%, 97.5% and 95.3%, 92.8%.92.8% respectively. There was no statistical difference according to age at diagnosis, site and metastatic/bifocal disease. During follow-up 13/59 patients (22%) revealed moderate (2)/slight (11) impairment of the pulmonary function at spirometry assessment. Audiometric tests were available for 59 patients: 42 were normal (71%), 11 had a slight deficit, 4 moderate and 2 severe. Neurocognitive homogeneous evaluations were available only for 9 patients, so no clear correlation can be done, except observing the lowest scores in the patient with basal ganglia involvement. New endocrine deficits appeared in 9 patients after the treatment. CONCLUSIONS WVI tailored on response to chemotherapy proved effective in curing children CNS germinoma. Cisplatin and bleomycin-containing regimens induce high-response rates with known but in our experience limited sides effects. New collaborative protocols will investigate the reduction of the doses of irradiation and the use of less toxic drugs in order to achieve the same cure rates with less side effects.

HGG-46. PEDIATRIC RADIATION-INDUCED GLIOMA PATIENT SAMPLES AND NOVEL PATIENT-DERIVED MODELS REVEAL TRANSLATIONALLY RELEVANT TREATMENT SUSCEPTIBILITIES AND POTENTIAL GERMLINE RISK FACTORS

Abstract BACKGROUND Pediatric radiation-induced glioma (RIG) is an incurable secondary high-grade glioma (HGG) afflicting up to 4% of children who previously received cranial radiotherapy (RT) for other malignancies. RIG accounts for up to 10% of pediatric brain tumor deaths. It has no known genetic risk factors nor effective treatment and is uniformly fatal, partly due to extremely limited available models. Our recent molecular characterization of patient samples showed that while RIG and primary pediatric HGG share histological similarities, their genetic alterations and gene expression profiles differ. METHODS We obtained germline DNA sequencing from 28 RIG patients and 112 matched controls who received RT but did not develop RIG. In addition, we developed cell culture and murine orthotopic patient-derived xenograft (PDX) models from four RIGs. We conducted single-cell RNA-seq (scRNA-seq), drug screening/validation, and CRISPR functional screening on our novel models. RESULTS Germline mutations in TP53, PARP10, POLI, DCLRE1A, and MLH3 were more common in RIG patients than controls (p&amp;lt;0.002). Our matched cell culture and PDX models of RIG represent the genetic diversity of the disease. The PDX models form tumors in 30-120 days and closely recapitulate human RIG by histology and scRNA-seq. They show susceptibility across models to DNA-damaging treatments (etoposide, irinotecan, radiation), as well as MEK, PARP, and proteasome inhibition, with orthogonal supporting findings via CRISPR screening. Several two-treatment combinations also show efficacy and synergy across models, including radiation and trametinib in vivo (logrank p=0.029). Discussion: RIG is an understudied but major cause of pediatric CNS tumor mortality that differs genetically from primary pediatric HGG. Our findings suggest specific germline alterations in DNA repair pathways may put some patients at higher risk of developing RIG after cranial RT. We also introduce the first set of patient-derived RIG models in order to advance translational RIG research, with characterization of translationally relevant treatment susceptibilities.

TRLS-16. RESULTS FROM SJDAWN: A ST JUDE CHILDREN’S RESEARCH HOSPITAL PHASE 1 STUDY EVALUATING MOLECULARLY DRIVEN DOUBLET THERAPIES FOR ALL CHILDREN WITH REFRACTORY OR RECURRENT CENTRAL NERVOUS SYSTEM (CNS) MALIGNANT NEOPLASMS AND YOUNG ADULTS WITH SHH MEDULLOBLASTOMA

Abstract BACKGROUND Pediatric CNS tumors have recurring molecular aberrations that modulate the cell cycle. We hypothesized that ribociclib, a brain-penetrant CDK4/6 inhibitor, given in doublet combinations could benefit patients with CNS malignancies. SJDAWN (NCT03434262) was launched to determine the recommended phase 2 dose (RP2D), safety, pharmacokinetics, and early efficacy of doublets. METHODS Patients &amp;gt;1 and &amp;lt;40 years with recurrent/refractory CNS malignancy were stratified into 3 strata. Escalating dose-levels in 28-day cycles were evaluated in each stratum by rolling-6 design with an expansion cohort at the highest tolerated dose-level. RP2D was declared if ≤3 dose-limiting toxicities (DLTs) occurred in 12 patients. Stratum A evaluated ribociclib/gemcitabine in group3/group4 (Grp3/4) MB and ependymoma (EPN). Stratum B evaluated ribociclib/trametinib in malignancies not eligible for stratum A or C. Stratum C evaluated ribociclib/sonidegib in skeletally mature patients with SHH-MB, TP53 wildtype with chr9q loss and/or PTCH1 mutation. Tumor, blood, and CSF samples were analyzed. RESULTS From 2018-2022, 68 patients enrolled: 33 in A (22 Grp3/4-MB, 11 EPN); 28 in B (15 HGG, 13 other); 7 SHH-MB in C. The RP2D was gemcitabine 1250mg/m2 IV day 1, 15 and ribociclib 350mg/m2 PO 1-21 days for A; trametinib 0.025mg/kg PO days 1-14 and ribociclib 280mg/m2 PO days 7-21 for B; and not established for C. DLTs included neutropenia (A), thrombocytopenia (B), mucositis (B), and rash (C). The 6-, 12-, and 24-month progression-free survival (PFS) was 42%(26%-58%), 18%(8%-33%), and 12%(4%-26%) in A, 18%(7%-34%), 4%(1%-15%), and 0% in B, 71%(30%-92%), 43%(13%-73%), and 0% in C. PFS beyond 2-years was observed in 3 Grp3/4-Subgroup3 MBs and 1 EPN. Amplification of CDK6, CCND2, and MYCN in serial CSF samples suggested a mechanism of resistance. CONCLUSIONS Ribociclib doublets are tolerated, and the lengthy survival of some patients suggests a selective benefit.

LMIC-08. NEUROSURGERY UTILIZATION RATE FOR PEDIATRIC LOW-GRADE GLIOMA: A SIMULATION-BASED ANALYSIS

Abstract BACKGROUND The outcomes of pediatric low-grade glioma (pLGG) are markedly influenced by accessibility to neurosurgical services. Even when clinically recommended, neurosurgical interventions might not be feasible when there is scarcity in qualified medical professionals and preparedness of medical facilities, which is the case in many low- and middle-income countries (LMICs). To aid cancer control planning efforts and guide policy makers and clinicians to prioritize allocation of resources, accurate neurosurgical utilization rate (NUR) estimations are crucial. This study developed a model to estimate the NUR, to facilitate the approximation of neurosurgery needs for pLGG. METHODS A decision tree model was developed to assess the NUR in HICs and LMICs. Patients were classified into five groups based on the anatomic site of the tumor. For each type of cancer, patients had three surgical options, gross total resection, subtotal resection, and biopsy. Anatomic distribution and likelihood to perform surgical resection were retrieved from the literature for both HICs and LMICs. RESULTS Findings showed discrepancy in the anatomic distribution of pLGG in HICs and LMICs. Proportion of patients with cerebral hemisphere, cerebellum, OPHG/diencephalon, brainstem, and spine tumors and their likelihood to undergo surgical intervention were 34% | 28%, 32% | 27%, 17% | 4%, 12% | 3% and 5% | 4% in HICs, and 26% | 22%, 39% | 32%, 26% | 5%, 6% | 2% and 3% | 2% in LMICs, respectively. Overall, NUR in pLGG patients was 66% in HICs and 63% in LMICs. CONCLUSION Despite the limited resources in LMICs, the overall proportion of patients recommended to undergo a surgical intervention is comparable to HICs. For this need to be met, long-term planning need to take place at the policymaking level. It is possible to estimate the NUR for all pediatric CNS tumors following the same approach to more comprehensively estimate the neurosurgical needs of this patient population globally.

EPID-08. PEDIATRIC GLIOMA IN INDONESIA: CLINICAL PROFILES AND OUTCOMES

Abstract BACKGROUNDS Gliomas are the most common form of pediatric brain tumor. The primary obstacle to optimizing pediatric brain tumor health services, particularly in LMICs, is the lack of comprehensive epidemiological data. We aim to compile comprehensive data on pediatric gliomas, focusing on clinical profiles and outcomes within a national general hospital in Indonesia. METHODS A retrospective observational longitudinal study was performed at Cipto Mangunkusumo National General Hospital, focusing on glioma patients’ profiles and outcomes, registered under the pediatric CNS tumor service from January 2022 to December 2023. RESULTS Out of 50 suspected glioma patients, 28 patients (56%) underwent biopsy, 28% underwent other modalities (brainstem location), 12% were scheduled for surgery but had already died, 2% were in a watchful waiting mode, and 2% were scheduled for surgery but were lost to follow-up. Glioma-confirmed patients were predominantly female (57.1%), with a mean age of 7.11 ± 4.98. Low-grade gliomas predominated at 57.1%, a trend we attribute to Cipto Mangunkusumo’s status as a referral national hospital, where low-grade glioma cases may have been managed more frequently at lower-level hospitals. The majority of tumors were supratentorial (53.6%) compared to infratentorial (39.3%) and supra-infratentorial (7.1%). The most common symptoms were seizures (25%), followed by headaches (21.4%), disequilibrium (14.3%), and vomiting (10.7%). Moreover, the latter three symptoms exhibited a longer mean delay between symptom onset and medical consultation, potentially impacting prognosis. In the last follow-up, higher-grade gliomas demonstrated a significantly higher mortality rate at 28.6% compared to low-grade gliomas at 3.6% (P &amp;lt; 0.001). CONCLUSION Given the variable clinical characteristics of glioma tumors, these results underscore the urgent need for comprehensive epidemiological data on pediatric gliomas in Indonesia, particularly regarding prognosis-related factors. Such data could serve as a crucial step towards future research and clinical strategies aimed at improving outcomes for children with gliomas.

LMIC-04. BUILDING PEDIATRIC NEURO-ONCOLOGY CAPACITY IN LMICS THROUGH MULTIDISCIPLINARY EDUCATION AND COLLABORATION

Abstract BACKGROUND The St. Jude Global Academy Neuro-Oncology Training Seminar (NOTS) is a course in pediatric neuro-oncology (PNO) designed for physicians from low-income and middle-income countries. The curriculum was systematically designed and includes 9 weeks of online learning and a 5-day in-person workshop. The NOTS has been run 3 times: 2019, 2022, and 2023. We sought to evaluate the outcomes of these courses. METHODS After the initial course where institutions were invited, applying institutions were selected based on the size of the neuro-oncology program, multidisciplinary representation, and perceived impact of the course. Data on course participants have been prospectively collected. A survey evaluating course impact was completed by graduates. RESULTS For 2022, 51 institutions from 29 countries applied and 15 were selected. In 2023, 60 institutions from 31 countries applied and 18 were selected. Overall, 41 institutions from 29 countries have participated in NOTS. Furthermore, 191 individuals, including 68 pediatric oncologists, 37 neurosurgeons, 22 radiation oncologists, 19 radiologists, 18 pathologists, and 27 other specialists have participated. Survey responses (n=39) describe that 47% did not have multidisciplinary tumor boards (MDTB) before NOTS. 55% of those institutions now have MDTB, all claiming to be influenced by their participation in NOTS. 89% of participants claim that multidisciplinary communication improved after the course. The participants of NOTS have continued to be engaged beyond the course through the creation of the Global Alliance in Pediatric Neuro-Oncology (GAPNO). GAPNO workstreams have included monthly cases discussions, a multisite retrospective review of medulloblastoma outcomes collecting &amp;gt;300 patients in 8 countries, and the design of a comprehensive tool to evaluate PNO services. CONCLUSIONS A multidisciplinary course focused on pediatric CNS tumors care for resource-limited settings can help expand international engagement in PNO. Furthermore, through multidisciplinary collaboration, the PNO community can be galvanized to expand activities in capacity building.

DEI-02. DIRECT PATIENT OUTREACH IN PEDIATRIC NEURO-ONCOLOGY TO IMPROVE ACCESS TO GENOMIC PROFILING – THE MAKE-AN-IMPACT PROGRAM

Abstract BACKGROUND Genomic profiling and precision medicine have revolutionized cancer care but are not accessible to all due to high costs, insurance issues, limited access to testing facilities or qualified personnel. We established a program providing free clinical genomic testing worldwide (Make-An-IMPACT) and report findings from the pediatric CNS tumor cohort. METHODS Following a referral from: (1) a physician, (2) a disease-specific advocacy group, or (3) submission of contact information through program website, patients were enrolled on an IRB-approved protocol (NCT01775072). CSF cell free DNA (cfDNA) and matched normal samples were analyzed using MSK-IMPACTTM, a New York State Department of Health authorized hybridization capture-based next-generation panel DNA sequencing clinical assay. If a driver mutation wasn’t reported, raw genomic data was reviewed. OncoKBTM was used to determine the level of evidence supporting the clinical actionability of genomic aberrations. RESULTS 24 patients (median age 7.5; range 0.1-20 years) were enrolled; 9 (38%) from 5 non-US countries and 6 (25%) from non-NYC US sites. African American and Hispanics constituted 8% and 13% of the cohort. Potentially actionable alterations were identified in 4/24 (17%) cases; 2/24 (8%) subsequently received matched therapy. In unbiopsied or non-diagnostic cases, a disease defining alteration was identified in 8/15 (53.3%). BRAF-KIAA1549 fusions were identified in 2/3 DLGNT patients and 1p loss in all 3. Both patients with BRAF fused DLGNT started targeted therapy with Trametinib, one of whom achieved a durable treatment response for 2.5 years. 3/8 patients with unbiopsied brainstem lesions had a H3.3K27M mutation, while 2 had non-H3.3K27M mutations detected (1 SMARCB1 deletion, 1 IDHR172G mutation) leading to treatment regimen changes. CONCLUSIONS This study captured a broad range of pediatric CNS malignancies with a diverse patient representation across geographic regions. CSF cfDNA profiling provided important diagnostic and therapeutic information reported in real time to patients and local physicians.