K27M-mutant Diffuse Midline Glioma Research Articles

Integrated analyses reveal two molecularly and clinically distinct subtypes of H3 K27M-mutant diffuse midline gliomas with prognostic significance

H3 K27M-altered diffuse midline gliomas (DMGs) are highly malignant tumours that arise in the midline structures of the CNS. Most DMGs carry an H3 K27M-mutation in one of the genes encoding for histone H3. Recent studies suggested that epigenetic subgroups of DMGs can be distinguished based on alterations in the MAPK-signalling pathway, tumour localisation, mutant H3-gene, or overall survival (OS). However, as these parameters were studied individually, it is unclear how they collectively influence survival. Hence, we analysed dependencies between different parameters, to define novel epigenetic, clinically meaningful subgroups of DMGs. We collected a multifaceted cohort of 149 H3 K27M-mutant DMGs, also incorporating data of published cases. DMGs were included in the study if they could be clearly allocated to the spinal cord (n = 31; one patient with an additional sellar tumour), medulla (n = 20), pons (n = 64) or thalamus (n = 33), irrespective of further known characteristics. We then performed global genome-wide DNA methylation profiling and, for a subset, DNA sequencing and survival analyses. Unsupervised hierarchical clustering of DNA methylation data indicated two clusters of DMGs, i.e. subtypes DMG-A and DMG-B. These subtypes differed in mutational spectrum, tumour localisation, age at diagnosis and overall survival. DMG-A was enriched for DMGs with MAPK-mutations, medullary localisation and adult age. 13% of DMG-A had a methylated MGMT promoter. Contrarily, DMG-B was enriched for cases with TP53-mutations, PDGFRA-amplifications, pontine localisation and paediatric patients. In univariate analyses, the features enriched in DMG-B were associated with a poorer survival. However, all significant parameters tested were dependent on the cluster attribution, which had the largest effect on survival: DMG-A had a significantly better survival compared to DMG-B (p < 0.001). Hence, the subtype attribution based on two methylation clusters can be used to predict survival as it integrates different molecular and clinical parameters.

PATH-03. FOXR2-OVEREXPRESSING CENTRAL NERVOUS SYSTEM (CNS) TUMORS EXHIBIT SUBSTANTIAL DIVERSITY ACROSS HISTOLOGICAL, MOLECULAR, AND CLINICAL DIMENSIONS

Abstract BACKGROUND FOXR2 activation is regarded as the pathognomonic molecular signature of CNS neuroblastoma. However, a comprehensive understanding of the landscape for CNS tumors exhibiting FOXR2 activation is lacking. METHODS Integrated histopathologic, molecular, and clinical data analysis of 36 FOXR2-overexpressing CNS tumors identified through screening of an institutional dataset. RESULTS FOXR2-overexpressing CNS tumors showed a broad anatomic distribution throughout the neuraxis. Of the 36 tumors, 17 (47.2%) were gliomas and 17 (47.2%) were embryonal tumors. The gliomas included 16 high-grade gliomas (eight histone H3 K27M-mutant diffuse midline gliomas, seven radiation-associated tumors, and one with MN1::PATZ1 fusion) and one pilocytic astrocytoma. The embryonal tumors included ten CNS neuroblastomas, six pineoblastomas, and one medulloblastoma. Two were difficult-to-classify high-grade neuroepithelial tumors. The gliomas and embryonal tumors demonstrated comparable FOXR2 expression based on normalized RNA-sequencing data. FOXR2-overexpressing gliomas, but not embryonal tumors, displayed diverse concomitant genetic alterations. The most common mechanisms of FOXR2 activation involved structural alterations leading to proximity effects, frequently incorporating non-canonical non-coding exons, followed by activation of the exon -3 promoter. Tumor location, histology, and concomitant alterations correlated with patient outcomes. While FOXR2-overexpressing gliomas were aggressive with a 5-year overall survival of 13.3%, FOXR2-overexpressing embryonal tumors showed a diverse prognosis. FOXR2-activated CNS neuroblastoma showed a 5-year overall survival of 100%. Pineoblastomas with FOXR2 activation in the PB-FOXR2 DNA methylation group showed a 3-year survival of 0% despite multimodal therapy. The one medulloblastoma patient in the cohort is alive at three years post-diagnosis. CONCLUSION FOXR2-overexpressing CNS tumors manifest significant histological, molecular, and clinical diversity and can occur as post-radiation tumors. Glioma histology and concomitant genetic alterations correlate with treatment resistance and inferior prognosis, while FOXR2-overexpressing embryonal tumors show more heterogeneous outcomes. Integrating histologic and molecular diagnostic approaches along with therapeutic interventions and clinical outcomes is imperative for accurate prognostication and optimal therapeutic decision-making.

DNA Methylation Profiles Are Stable in H3 K27M-Mutant Diffuse Midline Glioma Neurosphere Cell Lines.

Diffuse midline gliomas are among the deadliest human cancers and have had little progress in treatment in the last 50 years. Cell cultures of these tumors have been developed recently, but the degree to which such cultures retain the characteristics of the source tumors is unknown. DNA methylation profiling offers a powerful tool to look at genome-wide epigenetic changes that are biologically meaningful and can help assess the similarity of cultured tumor cells to their in vivo progenitors. Paraffinized diagnostic tissue from three diffuse intrinsic pontine gliomas with H3 K27M mutations was compared with subsequent passages of neurosphere cell cultures from those tumors. Each cell line was passaged 3-4 times and analyzed with DNA methylation arrays and standard algorithms that provided a comparison of diagnostic classification and cluster analysis. All samples tested maintained high classifier scores and clustered within the reference group of H3 K27M-mutant diffuse midline gliomas. There was a gain of 1q in all cell lines, with two cell lines initially manifesting the gain of 1q only during culture. In vitro cell cultures of H3 K27M-mutant gliomas maintain high degrees of similarity in DNA methylation profiles to their source tumor, confirming their fidelity even with some chromosomal changes.

ONC201 (Dordaviprone) in Recurrent H3 K27M-Mutant Diffuse Midline Glioma.

Histone 3 (H3) K27M-mutant diffuse midline glioma (DMG) has a dismal prognosis with no established effective therapy beyond radiation. This integrated analysis evaluated single-agent ONC201 (dordaviprone), a first-in-class imipridone, in recurrent H3 K27M-mutant DMG. Fifty patients (pediatric, n = 4; adult, n = 46) with recurrent H3 K27M-mutant DMG who received oral ONC201 monotherapy in four clinical trials or one expanded access protocol were included. Eligible patients had measurable disease by Response Assessment in Neuro-Oncology (RANO) high-grade glioma (HGG) criteria and performance score (PS) ≥60 and were ≥90 days from radiation; pontine and spinal tumors were ineligible. The primary end point was overall response rate (ORR) by RANO-HGG criteria. Secondary end points included duration of response (DOR), time to response (TTR), corticosteroid response, PS response, and ORR by RANO low-grade glioma (LGG) criteria. Radiographic end points were assessed by dual-reader, blinded independent central review. The ORR (RANO-HGG) was 20.0% (95% CI, 10.0 to 33.7). The median TTR was 8.3 months (range, 1.9-15.9); the median DOR was 11.2 months (95% CI, 3.8 to not reached). The ORR by combined RANO-HGG/LGG criteria was 30.0% (95% CI, 17.9 to 44.6). A ≥50% corticosteroid dose reduction occurred in 7 of 15 evaluable patients (46.7% [95% CI, 21.3 to 73.4]); PS improvement occurred in 6 of 34 evaluable patients (20.6% [95% CI, 8.7 to 37.9]). Grade 3 treatment-related treatment-emergent adverse events (TR-TEAEs) occurred in 20.0% of patients; the most common was fatigue (n = 5; 10%); no grade 4 TR-TEAEs, deaths, or discontinuations occurred. ONC201 monotherapy was well tolerated and exhibited durable and clinically meaningful efficacy in recurrent H3 K27M-mutant DMG.

P10.11.A CHARACTERISTICS OF DIFFUSE MIDLINE GLIOMA WITH H3 K27M MUTATION IN ADULTS

Abstract BACKGROUND H3 K27M-mutant diffuse midline gliomas (DMG) occur primarily in children but can also be encountered in adults. Adult H3 K27M-mutant DMG is a still challenging disease with no effective medical therapies. MATERIAL AND METHODS We retrospectively analyzed the characteristics and prognostic factors of 49 adult patients with intracranial midline gliomas treated in Kobe University Hospital from 2006 to 2022. RESULTS The median age at diagnosis in midline gliomas was 50.8 years (range: 17-83 y). All tumors were located in thalamus n=25, brainstem n=10, cerebellum n=14. Isocitrate dehydrogenase 1 (IDH1) and H3 K27M mutation was recognized in 6 and 16 patients, respectively, which was mutually exclusive. In all midline gliomas, the identification of H3 K27M mutation was significantly a poor prognosis factor (median 18.5 months vs 34.2 months, p=0.041). Among IDH1 wild-type midline gliomas, however, H3 K27M-mutant DMG had no worse overall survival (median 18.8 months vs 22.2 months, p=0.805). CONCLUSION H3 K27M-mutant DMG is considered as a distinct WHO Grade 4 regardless of histological features, but the biological properties of H3 K27M mutation is not yet defined in IDH1 wild-type midline gliomas in adults.

P11.46.A ACTION: A RANDOMIZED PHASE 3 STUDY OF DORDAVIPRONE (ONC201) IN PATIENTS WITH NEWLY DIAGNOSED H3 K27M-MUTANT DIFFUSE GLIOMA

Abstract BACKGROUND H3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults. While radiotherapy (RT) provides transient benefit, no effective systemic therapy is currently available and current standard of care is RT followed by monitoring. Dordaviprone (ONC201), a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 (DRD2) and agonist of the mitochondrial protease ClpP. An integrated pooled analysis of five open-label trials previously demonstrated efficacy in dordaviprone-treated patients with recurrent disease. This phase 3 trial will be the first randomized, controlled study evaluating ONC201 in patients with H3 K27M-mutant disease. MATERIAL AND METHODS ACTION (NCT05580562) is a randomized, double-blind, placebo-controlled, parallel-group, international Phase 3 study of ONC201 in patients with newly diagnosed H3 K27M-mutant diffuse glioma. Patients who have completed standard frontline radiotherapy will be randomized 1:1:1 to receive placebo, once-weekly dordaviprone, or twice-weekly dordaviprone on two consecutive days. Primary efficacy endpoints are overall survival (OS) and progression-free survival (PFS) in all participants; PFS will be assessed by response assessment in neuro-oncology-high grade glioma by blind independent central review. Other objectives include assessments of safety, additional efficacy endpoints, clinical benefit, quality of life, pharmacokinetics, biomarkers, and healthcare resource utilization. Eligible patients will have histologically confirmed H3 K27M-mutant diffuse glioma, a Karnofsky/Lansky performance status ≥70, and completed first-line radiotherapy. Eligibility will not be restricted based on age; however, patients must be ≥10 kg at time of randomization. Patients with a primary spinal tumor, diffuse intrinsic pontine glioma, leptomeningeal disease, or cerebrospinal fluid dissemination are not eligible. ACTION is currently enrolling in the United States, with additional sites to be open internationally in 2023.

TIPS-08 ACTION: A RANDOMIZED PHASE 3 STUDY OF DORDAVIPRONE (ONC201) IN PATIENTS WITH NEWLY DIAGNOSED H3 K27M-MUTANT DIFFUSE GLIOMA

Abstract BACKGROUND H3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults. While radiotherapy (RT) provides transient benefit, no effective systemic therapy is currently available and current standard of care is RT followed by monitoring. Dordaviprone (ONC201), a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 (DRD2) and agonist of the mitochondrial protease ClpP. An integrated pooled analysis of five open-label trials previously demonstrated efficacy in dordaviprone-treated patients with recurrent disease. This phase 3 trial will be the first randomized, controlled study evaluating ONC201 in patients with H3 K27M-mutant disease. METHODS ACTION (NCT05580562) is a randomized, double-blind, placebo-controlled, parallel-group, international Phase 3 study of ONC201 in patients with newly diagnosed H3 K27M-mutant diffuse glioma. Patients who have completed standard frontline radiotherapy will be randomized 1:1:1 to receive placebo, once-weekly dordaviprone, or twice-weekly dordaviprone on two consecutive days. Primary efficacy endpoints are overall survival (OS) and progression-free survival (PFS) in all participants; PFS will be assessed by response assessment in neuro-oncology-high grade glioma by blind independent central review. Other objectives include assessments of safety, additional efficacy endpoints, clinical benefit, quality of life, pharmacokinetics, biomarkers, and healthcare resource utilization. Eligible patients will have histologically confirmed H3 K27M-mutant diffuse glioma, a Karnofsky/Lansky performance status ≥70, and completed first-line radiotherapy. Eligibility will not be restricted based on age; however, patients must be ≥10 kg at time of randomization. Patients with a primary spinal tumor, diffuse intrinsic pontine glioma, leptomeningeal disease, or cerebrospinal fluid dissemination are not eligible. ACTION is currently enrolling in the United States, with international sites opening imminently.

A validated prognostic nomogram for patients with H3 K27M-mutant diffuse midline glioma

H3 K27M-mutant diffuse midline glioma (H3 K27M-mt DMG) is a rare, highly invasive tumor with a poor prognosis. The prognostic factors of H3 K27M-mt DMG have not been fully identified, and there is no clinical prediction model for it. This study aimed to develop and validate a prognostic model for predicting the probability of survival in patients with H3 K27M-mt DMG. Patients diagnosed with H3 K27M-mt DMG in the West China Hospital from January 2016 to August 2021 were included. Cox proportional hazard regression was used for survival assessment, with adjustment for known prognostic factors. The final model was established using the patient data of our center as the training cohort and data from other centers for external independent verification. One hundred and five patients were ultimately included in the training cohort, and 43 cases from another institution were used as the validation cohort. The factors influencing survival probability in the prediction model included age, preoperative KPS score, radiotherapy and Ki-67 expression level. The adjusted consistency indices of the Cox regression model in internal bootstrap validation at 6, 12, and 18 months were 0.776, 0.766, and 0.764, respectively. The calibration chart showed high consistency between the predicted and observed results. The discrimination in external verification was 0.785, and the calibration curve showed good calibration ability. We identified the risk factors that affect the prognosis of H3 K27M-mt DMG patients and then established and validated a diagnostic model for predicting the survival probability of these patients.

Abstract CT060: ACTION: A randomized phase 3 study of dordaviprone (ONC201) in patients with newly diagnosed H3 K27M-mutant diffuse glioma

Abstract Background: H3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults. While radiotherapy (RT) provides transient benefit, no effective systemic therapy is currently available and current standard of care is RT followed by monitoring. Dordaviprone (ONC201), a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 (DRD2) and agonist of the mitochondrial protease ClpP. An integrated pooled analysis of five open-label trials previously demonstrated efficacy in dordaviprone-treated patients with recurrent disease. This phase 3 trial will be the first randomized, controlled study evaluating dordaviprone in patients with H3 K27M-mutant disease. Methods: ACTION (NCT05580562) is a randomized, double-blind, placebo-controlled, parallel-group, international Phase 3 study of dordaviprone in patients with newly diagnosed H3 K27M-mutant diffuse glioma. Patients who have completed standard frontline radiotherapy will be randomized 1:1:1 to receive placebo, once-weekly dordaviprone, or twice-weekly dordaviprone on two consecutive days. Primary efficacy endpoints are overall survival (OS) and progression-free survival (PFS) in all participants; PFS will be assessed by response assessment in neuro-oncology-high grade glioma by blind independent central review. Other objectives include assessments of safety, additional efficacy endpoints, clinical benefit, quality of life, pharmacokinetics, biomarkers, and healthcare resource utilization. Eligible patients will have histologically confirmed H3 K27M-mutant diffuse glioma, a Karnofsky/Lansky performance status ≥70, and completed first-line radiotherapy. Eligibility will not be restricted based on age; however, patients must be ≥10 kg at time of randomization. Patients with a primary spinal tumor, diffuse intrinsic pontine glioma, leptomeningeal disease, or cerebrospinal fluid dissemination are not eligible. ACTION is currently enrolling in the United States, with additional sites to be open internationally in 2023. Citation Format: Isabel Arrillaga-Romany, Andrew Lassman, Susan L. McGovern, Sabine Mueller, Louis B. Nabors, Martin van den Bent, Michael Vogelbaum, Joshua E. Allen, Allen S. Melemed, Rohinton S. Tarapore, Dewen Yang, Patrick Wen, Timothy Cloughsey. ACTION: A randomized phase 3 study of dordaviprone (ONC201) in patients with newly diagnosed H3 K27M-mutant diffuse glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT060.

TB-1 ADDITIONAL GENETIC ALTERATIONS DIFFERENTIALLY ALTER THE TRANSCRIPTOMIC LANDSCAPE OF H3 K27M-MUTANT DIFFUSE MIDLINE GLIOMA

Abstract Histone H3 K27M mutation is a hallmark mutation for H3 K27M-mutant diffuse midline glioma (DMG), but targeting this mutation has yet to achieve a significant survival benefit in clinical trials. Recent analyses revealed alterations in several genes, such as NF1 and PDGFRA, are observed in substantial subpopulations of H3 K27M-mutant DMG patients in addition to H3 mutation and recurrent TP53 mutations, indicating patient-to-patient tumor heterogeneity and the potential necessity of tailored target therapy for the treatment of this disease. Here, using our human induced pluripotent stem cells (iPSC)-derived glioma avatar platform, we designed DMG models by introducing TP53R248Q with or without heterozygous H3 K27M mutation in combination with further genetic modifications of either NF1 knockout or PDGFRAD842V overexpression to recapitulate DMG subpopulations. Mice with TP53R248Q; H3F3AK27M (QM) tumors survived significantly longer than those harboring QM;NF1-/- (QMN) tumors and QM; PDGFRAD842Voe (QMP) tumors. RNA-sequencing of those induced DMG (iDMG) neurospheres revealed altered patterns of upregulation of MAPK pathway genes both in QMN and QMP-iDMG neurospheres compared to their H3 wildtype counterparts with the same combinations of genetic alterations, suggesting that those additional mutations modifies the oncogenic signaling associated with H3 K27M mutation. Further, differential expression analysis comparing QMN and QMP-iDMG neurospheres revealed 405 differentially expressed genes. Gene set enrichment analysis showed upregulation of transcriptional programs related to mesenchymal signature in QMN-iDMG neurospheres and proneural signature in QMP-iDMG neurosphere as expected. These data show that NF1 deletion and PDGFRAD842V overexpression significantly alter gene expression in H3 K27M-mutant iDMG tumors, potentially opening up a new therapeutic avenue in these devastating tumors with patient-to-patient heterogeneity. Further work using these models will shed light on the development of tailored therapy based on detailed genetic information on each patient sample, such as combining targeted kinase inhibition with HDAC inhibitors that have shown promise in the clinic.

MPC-16 CHARACTERISTICS AND PROGNOSTIC FACTORS OF H3K27M-MUTANT DIFFUSE MIDLINE GLIOMA

Abstract H3 K27M-mutant diffuse midline gliomas (DMG) is a still challenging disease with no effective medical therapies. We analyzed the characteristics and prognostic factors of 64 patients with midline gliomas including 18 patients with H3 K27M-mutant DMG treated in Kobe University Hospital from 2006 to 2021. The median age at diagnosis in midline gliomas was 50.1 years (range: 14-82 y). All tumors were located in thalamus n=25, corpus callosum n=8, brainstem n=8, spinal cord n=6, cerebellum n=15, and pineal region n=2. Isocitrate dehydrogenase 1 (IDH1) and H3 K27 mutation was recognized in 6 and 18 patients, respectively, which was mutually exclusive. In all midline gliomas, the identification of an H3 K27M mutation was significantly a poor prognosis factor (median 19.8 months vs 27.9 months, p=0.042). Compared to midline gliomas without histone H3 and IDH1 mutations (IDH1/H3 wild type), however, H3 K27M-mutant DMG had no worse overall survival (median 19.8 months vs 15.9 months, p=0.51). H3 K27M-mutant DMG is considered as a distinct WHO Grade 4 regardless of histological features, but the biological properties of H3 K27M mutation is not yet defined in IDH1 wild-type midline gliomas.

PATH-08. A COMPREHENSIVE GENOMIC STUDY OF 390 H3F3A-MUTANT PEDIATRIC-TYPE DIFFUSE HIGH-GRADE GLIOMAS WHO CNS GRADE 4

Abstract OBJECTIVES Histone gene mutant malignant gliomas - H3K27-altered diffuse midline glioma (DMG) and diffuse hemispheric glioma (DHG) H3G34-mutant - occur in all age groups and can have significant variation in clinical outcomes. Here, we report comprehensive genomic profiling from one of the largest collections of H3F3A-mutant gliomas analyzed to date, identifying subsets defined by recurrently co-mutated genes. METHODS We identified 390 H3F3A-mutant diffuse gliomas WHO grade 4 (201 females and 189 males) that were profiled in the comprehensive genomic profiling program at Foundation Medicine between 2013-2020. Information from pathology reports, histopathology reviews, and clinical data was assessed. RESULTS Our cohort comprised 304 (77.9%) H3K27M-mutant DMG WHO grade 4 (156 females and 148 males) and 86 H3G34-mutant DHG (45 females and 41 males) with a median age of 20 years (1-74 years). H3K27M-mutant DMG distributed equally between pediatric and adult patients, with 52% of the patients older than 20 years, 30% older than 30 years, and 18% older than 40 years at the time of first diagnosis. Clonal FGFR1 hotspot mutations were exclusively detected in K27M-mutant DMG (n = 64/304, 21%; p=0.0001), with a significant association with a higher age at first diagnosis (median 32.5 years), and with a wide tumor distribution across the diencephalon. Additional genes which were significantly more frequently altered in K27M-mutant compared to G34-mutant diffuse gliomas included NF1 (31% vs. 8.1%; p=0.0001) and PIK3CA/PIK3R1 (27.9% vs. 15.1%; p=0.016). Conversely, targetable alterations of the cell-cycle pathway (CDK4/6 amplifications and CDKN2A/B deletions) were enriched in H3G34-mutant DHG (26%) compared to H3K27M-mutant DMG (7%). Potentially targetable PDGFR alterations were present in 32.5% of H3G34-mutant DHG and in 18% of H3K27M-mutant DMG. CONCLUSIONS These data expand our understanding of the tumor-specific molecular features of pediatric-type high-grade gliomas, identifying cohort sub-structure by recurrent co-mutations, which can inform diagnosis and clinical trial design.

RTID-01. ONC108: A RANDOMIZED PHASE 3 STUDY OF ONC201 IN PATIENTS WITH NEWLY DIAGNOSED H3 K27M-MUTANT DIFFUSE GLIOMA

Abstract BACKGROUND H3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults; while radiotherapy (RT) provides transient benefit, no effective systemic therapy is currently available. ONC201, a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 (DRD2) and agonist of the mitochondrial protease ClpP. An integrated pooled analysis of objective response in ONC201-treated patients enrolled in one of five open-label trials has previously demonstrated efficacy in patients with recurrent disease. This phase 3 trial will be the first randomized, controlled study evaluating ONC201 in patients with H3 K27M-mutant disease. METHODS ONC108 is a randomized, double-blind, placebo-controlled, parallel-group, international Phase 3 study of ONC201 in patients with newly diagnosed H3 K27M-mutant diffuse glioma. Patients will be randomized to receive once-weekly ONC201 or placebo following standard frontline radiotherapy. Primary efficacy endpoints are overall survival (OS) and progression-free survival (PFS) in all participants; PFS will be assessed with the response assessment in neuro-oncology-high grade glioma by blind independent central review. Other objectives include assessments of safety, additional efficacy endpoints, clinical benefit, quality of life, pharmacokinetics, biomarkers, and healthcare resource utilization. Eligible patients will have histologically confirmed H3 K27M-mutant diffuse glioma, a Karnofsky/Lanksy performance status ≥ 70, and completed first-line radiotherapy. Eligibility will not be restricted based on age; however, patients must be ≥ 10 kg at time of randomization. Patients with a primary spinal tumor, diffuse intrinsic pontine glioma, leptomeningeal disease, or cerebrospinal fluid dissemination are not eligible.

Simultaneous Integrated Boost Technique for Pediatric High-Grade Gliomas: A Single-Institution Experience

<h3>Purpose/Objective(s)</h3> The prognosis for pediatric patients with high grade glioma (HGG) remains dismal despite aggressive multidisciplinary treatment, and there is marked variability regarding the optimal radiation approach. We report outcomes from a retrospective review of pediatric patients with HGG treated using a simultaneous integrated boost (SIB) technique at a single institution. <h3>Materials/Methods</h3> The medical records of patients ages 0–22y with biopsy-proven non-DIPG localized HGG treated with radiotherapy (RT) from January 2006 to May 2021 were retrospectively reviewed on an IRB approved protocol. Endpoints were Kaplan-Meier estimates of overall survival (OS) and progression free survival (PFS), and patterns of failure. <h3>Results</h3> There were 32 patients in the cohort; 24 patients had glioblastoma without further molecular characterization, 2 had H3 K27M mutant diffuse midline gliomas, 2 had G34R mutant glioma, 2 had glioblastoma with IDH1 mutation, 1 had high-grade astrocytoma, and 1 had high-grade glial neoplasm. Median age at diagnosis was 14.9 (1.9–21.5) years. Prior to RT, 6 patients obtained both spinal MRIs and lumbar punctures, 5 obtained spinal MRIs, and 1 had a lumbar puncture; none had evidence of distant metastases. All patients were treated with intensity modulated radiotherapy (IMRT) using SIB with two dose levels. The most common (n=25) dose to the high dose volume was 60 Gy (range, 40–60 Gy); the most common (n=24) dose to the low dose volume was 50 Gy (range, 30–55 Gy). Treatment was most commonly (n=26) delivered in 30 fractions (range, 15-33). One patient did not complete planned RT due to tumor hemorrhage. Median follow up for all patients was 17 (0–164.4) months. For patients who completed planned RT, median PFS was 20.1 (1–140) months from RT start. Median OS was 25.9 months with one- and two-year survival rates of 80% and 56%, respectively. Of 19 patients with known recurrence, 8 recurred locally, 7 recurred in the distant brain, and 4 developed leptomeningeal dissemination. Three patients were alive at 10 years after initial diagnosis; none of these patients were known to have tumors with IDH mutations. <h3>Conclusion</h3> This study explores outcomes in a cohort of pediatric HGG patients treated with SIB technique, with encouraging initial results. Future efforts will be necessary to identify additional molecular and treatment factors that impact outcome.

P04.04.A A comprehensive genomic study of 390 H3F3A-mutant pediatric-type diffuse high-grade gliomas WHO CNS grade 4

Abstract Background Histone gene mutant malignant gliomas - H3K27-altered diffuse midline glioma (DMG) and diffuse hemispheric glioma (DHG) H3G34-mutant - occur in all age groups and can have significant variation in clinical outcomes. Here, we report comprehensive genomic profiling from one of the largest collections of H3F3A-mutant gliomas analyzed to date, identifying subsets defined by recurrently co-mutated genes. Material and Methods We identified 390 H3F3A-mutant diffuse gliomas WHO grade 4 (201 females and 189 males) that were profiled in the comprehensive genomic profiling program at Foundation Medicine between 2013-2020. Information from pathology reports, histopathology review, and patient clinical data was assessed Results Our cohort comprised 304 (77.9%) H3K27M-mutant DMG WHO grade 4 (156 females and 148 males) and 86 H3G34-mutant DHG (45 females and 41 males) with a median age of 20 years (1- 74 years). H3K27M-mutant DMG distributed equally between pediatric and adult patients, with 52% of the patients older than 20 years, 30% older than 30 years, and 18% older than 40 years at the time of first diagnosis. Clonal FGFR1 hotspot mutations were exclusively detected in K27M-mutant DMG (n = 64/304, 21%; p=0.0001), with a significant association with a higher age at first diagnosis (median 32.5 years), and with a wide tumor distribution across the diencephalon. Additional genes which were significantly more frequently altered in K27M-mutant compared to G34-mutant diffuse gliomas included NF1 (31% vs. 8.1%; p=0.0001) and PIK3CA/PIK3R1 (27.9% vs. 15.1%; p=0.016). Conversely, targetable alterations of the cell-cycle pathway (CDK4/6 amplifications and CDKN2A/B deletions) were enriched in H3G34-mutant DHG (26%) compared to H3K27M-mutant DMG (7%). Potentially targetable PDGFR alterations were present in 32.5% of H3G34-mutant DHG and in 18% of H3K27M-mutant DMG. Conclusion These data expand our understanding of the tumor-specific molecular features of pediatric-type high-grade gliomas, identifying cohort sub-structure by recurrent co-mutations, which can inform diagnosis and clinical trial design.

National-level overall survival patterns for molecularly-defined diffuse glioma types in the United States.

Molecularly-defined diffuse glioma types-including IDH-wildtype glioblastoma, IDH-mutant astrocytoma, IDH-mutant 1p/19q-codeleted oligodendroglioma, and H3 K27M-mutant diffuse midline glioma-were incorporated into U.S. cancer registry reporting for individuals with brain tumors beginning in 2018. We leveraged these new data to estimate the national-level overall survival (OS) patterns associated with glioma integrated diagnoses. Individuals diagnosed with diffuse gliomas in 2018 and had brain molecular marker data were identified within the U.S. National Cancer Database. OS was estimated using Kaplan-Meier methods and stratified by WHO CNS grade, age, sex, tumor size, treatment, extent of resection, and MGMT promoter methylation. Additionally, the effects of WHO CNS grade were examined among individuals with IDH-wildtype astrocytic gliomas. 8651 individuals were identified. One-year OS was 53.7% for WHO grade 4 IDH-wildtype glioblastomas; 98.0%, 92.4%, and 76.3% for WHO grade 2, 3, and 4 IDH-mutant astrocytomas, respectively; 97.9% and 94.4% for WHO grade 2 and 3 IDH-mutant 1p/19q-codeleted oligodendrogliomas, respectively; and 55.9% for H3 K27M-mutant diffuse midline gliomas. Among IDH-wildtype glioblastomas, median OS was 17.1 months and 12.4 months for methylated and unmethylated MGMT promoters. Additionally, IDH-wildtype diffuse astrocytic gliomas reported as WHO grade 2 or 3 demonstrated longer OS compared to grade 4 tumors (both P < .001). Our findings provide the initial national OS estimates for molecularly-defined diffuse gliomas in the United States and illustrate the importance of incorporating such data into cancer registry reporting.

SYST-07 WINDOW-OF-OPPORTUNITY STUDY OF ONC201 IN PEDIATRIC PATIENTS WITH DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG) AND THALAMIC GLIOMA

BACKGROUNDH3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults; no effective systemic therapy is available. ONC201, a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 and agonist of the mitochondrial protease ClpP. ONC201 monotherapy demonstrated durable objective responses in adults with recurrent H3 K27M-mutant glioma. This phase 1 trial will evaluate ONC201±radiotherapy (RT) in pediatric patients with H3 K27M-mutant midline glioma DIPG. METHODSThis multicenter, open-label, dose escalation and expansion phase 1 study of ONC201 is comprised of eight arms that will evaluate the recommended phase 2 dose (RP2D) of ONC201, biomarkers, and pharmacokinetics (PK) of ONC201±RT in various treatment settings (NCT03416530). Arm G previously defined the RP2D for twice-weekly ONC201 on consecutive days. Arm H, for which enrollment is ongoing, will estimate the influence of tumor location and blood-brain barrier integrity on PK and intratumoral ONC201 exposure in biopsy-eligible pediatric tumors (DIPG or contrast-enhancing thalamic glioma). Patients eligible for Arm H will be aged 2-≤19 years, ≥2 weeks from last RT administration, and have a KPS/LPS ≥50; prior confirmation of H3 K27M mutation is not required. In Arm H, single-agent ONC201 administration will occur twice-weekly on consecutive days during each 21-day cycle at the RP2D defined in Arm G. Arm H has a planned enrollment of 27 patients (DIPG, n=15; thalamic glioma, n=12), with three patients undergoing a single biopsy at each of the following time points: 1-3 h post-first dose, 22-26 h post-second dose, 1-3 h post-first dose, 6-10 h post-second dose, and 22-26 h post-second dose. The 22-26 h post-first dose biopsy in thalamic glioma was previously collected and will not be assessed in this treatment arm. Plasma for PK analysis will be collected from all patients.

Risk stratification of H3 K27M-mutant diffuse midline gliomas based on anatomical locations: an integrated systematic review of individual participant data.

The prognostic significance and genetic characteristics of H3 K27M-mutant diffuse midline gliomas (DMGs) in different anatomical locations requires further clarification. In this study, the authors integrated published data to investigate the differences between brainstem, thalamic, and spinal cord tumors. PubMed and Web of Science databases were used to search for eligible articles. Studies were included if they provided individual patient data of H3 K27M-mutant DMGs with available tumor locations. Hazard ratios (HRs) and 95% confidence intervals (CIs) were computed to investigate the survival of each subgroup. Eight hundred four tumors were identified, including 467, 228, and 109 in the brainstem, thalamus, and spine, respectively. Brainstem tumors were primarily observed in young children, while patients with thalamic and spinal cord tumors afflicted older patients. The Ki-67 labeling index was highest in brainstem tumors. Compared to patients with brainstem tumors, those with thalamic (HR 0.573, 95% CI 0.463-0.709; p < 0.001) and spinal cord lesions (HR 0.460, 95% CI 0.341-0.621; p < 0.001) had a significantly better survival. When patients were stratified by age groups, superior overall survival (OS) of thalamic tumors was observed in comparison to brainstem tumors in young children and adolescents, whereas adult tumors had uniform OS regardless of anatomical sites. Genetically, mutations in HIST1H3B/C (H3.1) and ACVR1 genes were mostly detected in brainstem tumors, whereas spinal cord tumors were characterized by a higher incidence of mutations in the TERT promoter. This study demonstrated that H3 K27M-mutant DMGs have distinct clinical characteristics, prognoses, and molecular profiles in different anatomical locations.

DIPG-29. Highly multiplexed digital spatial profiling of the tumor immune environment of pediatric and adultH3 K27M-mutant diffuse midline gliomas

Abstract BACKGROUND: H3 K27M-mutant diffuse midline gliomas (DMGs) are highly aggressive malignancies of the central nervous system that affect both pediatric and adult populations. The immune layout and genetic changes within the tumor microenvironment associated with these high-grade malignancies are thought to play an integral role in the phenotypic differences in tumor presentation and clinical course between both populations. Comparative immune landscape between pediatric and adult DMGs is not known. METHODS: The NanoString GeoMxTM Digital Spatial Profiler platform was used to determine the immune marker and genetic layout in a cohort of both pediatric and adult H3 K27M-mutant DMG tissue samples. Three fluorescently labeled antibodies targeting immune cells (CD45), epithelial cells (PanCK), tumor cells (H3 K27M) and a nucleic acid stain (SYTO-13) were used to identify and separate out the various components within the tumor tissues from selected regions of interest. The resultant information was then pooled into libraries that were run through the Illumina sequencing system to assess gene expression and proteomics for both cohorts of samples. RESULTS: Our data revealed that there were immune and genetic marker changes that were seen within both populations across multiple regions of interest within the tumor tissues. A number of immune cell types and protein markers exhibited significant difference between the pediatric and adult tissue cohorts. CONCLUSION: The digital spatial analysis of pediatric and adult H3 K27M-mutant DMGs show different immune and genetic profiles which are proposed to contribute to the clinical differences between both populations. These observed differences may play a role in future treatments for H3 K27M-mutant DMGs and further research is needed to explore this.

DIPG-28. IndolentH3 K27M-mutant diffuse midline glioma

Abstract INTRODUCTION: H3 K27M-mutant diffuse midline glioma (DMG) is an aggressive central nervous system tumor that is universally fatal with a median survival of 8-12 months after diagnosis. Here we present a patient who was incidentally found to have a lesion within the right thalamus on brain magnetic resonance imaging (MRI). Twelve years later, she was found to have a brain mass within the same area with pathology consistent with an H3 K27M-mutant DMG. CASE DESCRIPTION: A 14-year-old female presented with new onset left-sided numbness and weakness, blurry vision and a right-sided temporal headache. Her past medical history is significant for severe persistent asthma and anoxic brain injury secondary to a cardiopulmonary arrest at 2-years-of-age due to an asthma exacerbation. She has had multiple MRIs of her brain since her initial insult which initially showed the presence of a T2/FLAIR hyper-intense lesion within the right medial thalamus in addition to chronic central nervous system changes. The right thalamic lesion was stable in size between images obtained at 2-years and 4-years of age. Her current physical exam is significant for decreased strength to her left upper and lower extremities. Brain MRI with and without contrast is obtained with partial effacement of the third ventricle due to mass effect from an enlarging mass from the right thalamus. Biopsy of the lesion demonstrated an H3 K27M-mutant DMG, WHO grade IV. Our patient went on to receive palliative radiation therapy with 59.4 Gy over 33 fractions. DISCUSSION: This case illustrates an unusual presentation of an H3 K27M-mutant DMG with an indolent course, diagnosed twelve years after the initial MRI finding. This proposes the possibility of multiple factors playing a role in the oncogenesis of these aggressive tumors and that further research is warranted.