The Alliance AMBUSH Trial: Rationale and Design

Unlike medulloblastoma (MB) in children, robust prospective trials have not taken place for older patients due to the low incidence of MB in adults and adolescent and young adults (AYA). Current MB treatment paradigms for older patients have been extrapolated from the pediatric experience even though questions exist about the applicability of these approaches. Clinical and molecular classification of MB now provides better prognostication and is being incorporated in pediatric therapeutic trials. It has been established that genomic alterations leading to activation of the sonic hedgehog (SHH) pathway occur in approximately 60% of MB in patients over the age of 16 years. Within this cohort, protein patched homolog (PTCH) and smoothened (SMO) mutations are commonly found. Among patients whose tumors harbor the SHH molecular signature, it is estimated that over 80% of patients could respond to SHH pathway inhibitors. Given the advances in the understanding of molecular subgroups and the lack of robust clinical data for adult/AYA MB, the Alliance for Clinical Trial in Oncology group developed the AMBUSH trial: Comprehensive Management of AYA and Adult Patients with Medulloblastoma or Pineal Embryonal Tumors with a Randomized Placebo Controlled Phase II Focusing on Sonic Hedgehog Pathway Inhibition in SHH Subgroup Patients (Adult & Adolescent MedulloBlastoma Using Sonic Hedgehog Trial). This trial will enroll patients 18 years of age or older with MB (any molecular subgroup and risk stratification) or pineal embryonal tumor. Patients will be assigned to one of three cohorts: (1) average risk non-SHH-MB, (2) average risk SHH-MB, and (3) high risk MB or pineal embryonal tumors. All patients will receive protocol-directed comprehensive treatment with radiation therapy and chemotherapy. Patients with SHH-MB in cohort 1 will be randomized to a smoothened inhibitor or placebo as maintenance therapy for one year.

Epidemiology, Clinical Presentation, and Prognosis of Pediatric Brain Tumors: Experience of National Center for Children’s Health

Objective Brain tumors have become the most common solid tumors in children. The epidemiology is poorly described in China. This retrospective study aimed to describe the epidemiologic characteristics, clinical presentation, and prognosis in national health center for children. Method From January 2015 to December 2020, 484 cases age 0-18 years old diagnosed with brain tumors and receiving neurosurgery treatment were enrolled into the database. Pathology was based on the World Health Organization 2012 nervous system tumor classification, and tumor behavior were classified on International Classification of Diseases for Oncology, third edition. A descriptive and comparative statistic was performed on clinical manifestation, symptom duration, sex, age, tumor location, tumor behavior, and survival time. Results Among the 484 brain tumors, the median age at diagnosis was 4.62 [2.19, 8.17] years old (4.07 [1.64, 7.13] for benign tumors and 5.36 [2.78, 8.84] for malignant tumors). The overall male to female ratios were 1.33:1, with 1.09:1 and 1.62:1 for benign and malignant tumors respectively. Nausea and vomiting, headache were the most frequent initial symptoms. The median symptoms duration was 4[2, 21] weeks. The three most frequent tumor type were embryonal tumors (22.45%), other astrocytic tumors (20.17%), and diffuse astrocytic tumors (11.02%). Supratentorial tumors comprise 57.38% of all brain tumors. And the most common tumor locations were cerebellum and forth ventricles (38.67%), sellar region (22.87%) and ventricles (10.60%). Male were more common among choroid plexus tumors (63.64%), embryonal tumors (61.11%), ependymal tumors (68.57%), and germ cell tumors (78.13%). Patients were followed for 1 to 82 months. The overall 5-year survival was 77.4%, with 90.0% for benign tumor and 65.3% for malignant tumors. log-rank test found significant different at p <0.001 level. Conclusion Brain tumors presented particularly sexual, age dependent, and regional dependent epidemiological characteristic. Our results were consistent with previous reports, and might reflect the real epidemiology status in China.

Endogenous Retroviral Elements in Human Development and Central Nervous System Embryonal Tumors

Human endogenous retroviruses (HERVs), which are critical to normal embryologic development and downregulated during normal maturation, have been implicated in a variety of cancers. Abnormal persistent production of HERVs has been suggested to play a role in oncogenesis and to confer stem cell properties to cells. We recently demonstrated that the most recently incorporated HERV element (HERV-K HML-2) has been associated with the pathogenesis of the embryonal atypical teratoid rhabdoid tumor (AT/RT), shifting our understanding of embryonal tumor development. HML-2 expression is vital for proper human development and its expression is suppressed via methylation or chromatin remodeling as cells differentiate. We previously found that dysfunctional chromatin remodeling due to loss of SMARCB1 expression induces HML-2 envelope (env) expression, impairing cellular differentiation and migration, and facilitating tumor growth in AT/RT. Epigenetic dysregulation in other embryonal tumors with concomitant expression of stem-cell markers may facilitate HML-2 expression. Future studies could utilize HML-2 as potential diagnostic criteria, use its expression as a treatment biomarker, and investigate the efficacy of therapies targeting cells with high HML-2 expression.

MPC-5 Characteristics of H3 G34-mutant gliomas

Introduction: Diffuse hemispheric gliomas, H3 G34-mutant (DHG H3G34-mutant) are newly recognized infiltrating gliomas of the cerebral hemispheres of pediatric and young adult patients. We experienced 6 DHG H3G34-mutant cases. In this study, we describe the clinical, radiological and pathological characteristics of these cases. Result: Mean age at diagnosis was 16.8 years (range:10–26). Three patients were male. Among six cases, tumors located in cerebral cortex in five cases and multiple sites including basal ganglia and cortex in a case. All tumors showed no or only a faint contrast-enhancement and harbored restriction of diffusion. One patient underwent total resection, four underwent partial resection and one underwent biopsy. Pathological diagnosis were CNS embryonal tumors (n=3/6), glioblastoma, IDH-wildtype (n=2/6) and anaplastic astrocytoma, IDH-wildtype (n=1/5). All cases were negative for Olig2 and positive for GFAP in immunohistochemistry. Mean Ki-67 index was 38% (range: 10–60%). All cases revealed at least one of mitosis, necrosis or microvascular proliferation. Especially, mitosis was the most frequently found (n=5/6). The H3F3A mutations were G34R mutations in all cases. One case revealed a characteristic mutation pattern, therefore now we are performing further examination. Adjuvant chemoradiotherapies were performed for all cases. Mean progression free survival was 10.1 months (range: 1.6–33.1). Discussion: As published literatures reported, all cases exhibited restriction of diffusion and negative for Olig2. For a cerebral hemispheric tumor of pediatric or young adult patient which shows restriction of diffusion and no contrast-enhancement, and of which pathological findings is malignant and olig2 is negative, genetic analysis of H3F3A gene might be essential.

BIOM-42. IMMUNOHISTOCHEMICAL ASSESSMENT OF MEMBRANOUS SOMATOSTATIN TYPE 2A RECEPTOR (SST2A) EXPRESSION ACROSS HIGH-RISK PEDIATRIC CENTRAL NERVOUS SYSTEM (CNS) TUMORS

INTRODUCTION 77Lu-DOTATATE, a radionuclide therapy which binds SST2A, has demonstrated efficacy in neuroendocrine tumors and evidence of CNS penetration, supporting potential expansion within pediatric neuro-oncology. Understanding the prevalence of SST2A expression across pediatric CNS tumors is essential to identify patients who may benefit from somatostatin receptor-targeted therapy and to further elucidate the oncogenic role of SST2A. METHODS SST2A immunohistochemistry (IHC) was performed on tumor specimens and interpreted by two experienced pathologists (blinded), utilizing semi-quantitative scoring of membranous expression within viable tumor. Immunoreactive cell percentage was visually scored as 0 (none), 1 (&lt; 10%), 2 (10-50%), 3 (51-80%), or 4 (&gt;80%). Staining intensity was scored as 0 (none), 1 (weak), 2 (moderate), or 3 (strong). Combined scores for each specimen were calculated by multiplying percent immunoreactivity and staining intensity values (range=0-12). RESULTS A total of 117 tumor samples from 113 patients were analyzed. Significant differences in SST2A IHC scores were observed across histopathologic diagnoses, with consistently high scores in medulloblastoma (mean±SD=7.6±3.6 [n=36]) and meningioma (5.7±3.4 [n=15]), compared to minimal or absent expression in ATRT (0.3±0.6 [n=3]), ETMR (1.0±0 [n=3]), ependymoma (grades I-III; 0.2±0.7 [n=26]), and high-grade glioma (grades III-IV; 0.4±0.7 [n=22]). Pineoblastoma (3.8±1.5 [n=4]) and other embryonal tumors (2.3±3.8 [n=8]) exhibited intermediate, variable expression. Among expressors, there was no association between SST2A IHC score and patient age, sex, presence of metastases, likelihood of relapse, or prior treatment. In a subset of paired primary and recurrent specimens from 3 patients, SST2A IHC scores remained largely unchanged. Among medulloblastomas, SST2A IHC scores were higher in non-SHH (8.6±3.2) than SHH (5.0±3.3) molecular subgroups (p=0.033). CONCLUSIONS High membranous SST2A expression was demonstrated in medulloblastoma, meningioma, and some rarer embryonal tumors with potential diagnostic, biologic, and therapeutic implications. Somatostatin receptor-targeted therapy such as 177Lu-DOTATATE deserves further investigation in these highly SST2A-expressing pediatric CNS tumors.

EPID-21. EPIDEMIOLOGY AND RISK FACTORS OF PRIMARY CENTRAL NERVOUS SYSTEM (CNS) TUMORS IN CHILDREN AND ADULTS IN THE MIAMI CANCER INSTITUTE (MCI) COHORT

BACKGROUND Many epidemiological studies assess risk factors and incidence of primary CNS tumors in the United States; few describe the incidence in specific geographic locations. Environmental or ethnic/racial factors may affect the incidence of primary CNS tumors. Miami-Dade County (MDC) is an ethnically-diverse US county, with 69.4% Hispanic, 12.9% White Non-Hispanic, 15.5% Black Non-Hispanic, Asian 1.6%, 0.3% Native, and 0.3% other. We characterized primary CNS tumors at Miami Cancer Institute (MCI) relative to national reports. METHODS We reviewed electronic medical records for all patients (n=1221) diagnosed with CNS tumors at MCI from 2017 to 2021. Descriptive and statistical analyses assessed environmental and clinical variables. RESULTS Malignant CNS tumors account for 74% of MCI primary CNS tumors. Diffuse gliomas (41%), meningiomas (26%), and embryonal tumors (5%) were the most common histologies; embryonal tumors most common at younger ages (median: 18 years). The most abundant histological subtypes were glioblastoma (54%), benign meningioma (92%), and medulloblastoma (73%), respectively. Ethnic/racial composition of glioma patients at MCI was 55.9% Hispanic, 24.6% White Non-Hispanic, 6.4% Black Non-Hispanic, 1.8% Other Non-Hispanic, 1.3% Asian, 10% unreported, comparable to MDC. Compared to national averages, the age distribution at MCI was higher among lower grade gliomas (range: 15-96, Median: 61 years), yet lower for malignant gliomas (range: 1-93, median: 47 years). The incidence of malignant CNS tumors did not differ by gender; benign primary CNS tumors were significantly more frequent in females (245/324, 76%; p&lt; 0.001). Smoking history did not associate with incidence of primary CNS tumors; 793/1221 (65%) self-reported as non-smoker. CONCLUSION The ethnic/racial composition and incidence of primary CNS tumors by histology at MCI significantly differs from national CBTRUS database (Ostrom et al). This cohort will be further characterized by genetic profiles, race, diet, allergies, family history, substance use, clinical trial enrollment, therapeutic modalities, and overall survival rate.

Inferior vena cava and right atrial thrombosis in children with embryonal tumors

Tumor thrombosis of the central venous system in children with embryonal tumors is a rare complication, requiring a comprehensive treatment approach, with chemotherapy and the intervention of a multidisciplinary team of oncologists and cardiac surgeons. The article describes the medical history of a 9-month-old patient with bilateral nephroblastoma and tumor thrombosis of inferior vena cava and right atrium, as well as provides a brief review of the literature. The patient's parents gave their consent to the use of their child's data, including photographs, for research purposes and in publications.

Development of GPC2-directed chimeric antigen receptors using mRNA for pediatric brain tumors

Pediatric brain tumors are the leading cause of cancer death in children with an urgent need for innovative therapies. Here we show that the neuroblastoma cell surface oncoprotein glypican 2 (GPC2) is also highly expressed on multiple lethal pediatric brain tumors, including medulloblastomas, embryonal tumors with multi-layered rosettes, other CNS embryonal tumors, as well as a subset of highly malignant gliomas including H3 G35 mutant gliomas and some H3 K28M diffuse midline gliomas. To target GPC2 on these pediatric brain tumors with adoptive cellular therapies and to mitigate potential inflammatory neurotoxicity, we developed four mRNA chimeric antigen receptor (CAR) T cell constructs using the highly GPC2-specific, fully human D3 scFv that targets a conformational epitope on human and murine GPC2. First, we validated and prioritized these GPC2-directed mRNA CARs using in vitro cytotoxicity and T cell degranulation assays with GPC2-expressing neuroblastoma cells. Next, we expanded the testing of the two most potent GPC2-directed CAR constructs (D3V3 and D3V4) prioritized from these studies to GPC2-expressing medulloblastoma and high-grade glioma models, showing significant GPC2-specific cell death in multiple medulloblastoma and HGG cellular models. Finally, locoregional delivery of both GPC2-directed mRNA CAR T cells induced significant and sustained tumor regression in two orthotopic medulloblastoma models, and significantly prolonged survival in an aggressive orthotopic thalamic diffuse midline glioma model. No GPC2-directed CAR T cell related neurologic or systemic toxicity was observed. Taken together, these data show that GPC2 is a highly differentially expressed cell surface protein on multiple malignant pediatric brain tumors that can be targeted safely with local delivery of mRNA CAR T cells.