Development of Chromosome 1q+ Specific Treatment for Highest Risk Pediatric Posterior Fossa Ependymoma

PURPOSE

There are no effective treatment strategies for children with highest-risk posterior fossa group A ependymoma (PFA). Chromosome 1q gains (1q+) are present in approximately 25% of newly diagnosed PFA tumors, and this number doubles at recurrence. Seventy percent of children with chromosome 1q+ PFA will die because of the tumor, highlighting the urgent need to develop new therapeutic strategies for this population.

EXPERIMENTAL DESIGN

In this study, we utilize 1q+ PFA in vitro and in vivo models to test the efficacy of combination radiation and chemotherapy in a preclinical setting.

RESULTS

5-fluorouracil (5FU) enhances radiotherapy in 1q+ PFA cell lines. Specifically, 5FU increases p53 activity mediated by the extra copy of UCK2 located on chromosome 1q in 1q+ PFA. Experimental downregulation of UCK2 resulted in decreased 5FU sensitivity in 1q+ PFA cells. In in vitro studies, a combination of 5FU, retinoid tretinoin (ATRA), and radiation provided the greatest reduction in cellular proliferation and greatest increase in markers of apoptosis in 1q+ PFA cell lines compared with other treatment arms. Similarly, in vivo experiments demonstrated significant enhancement of survival in mice treated with combination radiation and 5FU and ATRA.

CONCLUSIONS

These results are the first to identify a chromosome 1q+ specific therapy approach in 1q+ PFA. Existing phase I studies have already established single-agent pediatric safety and dosages of 5FU and ATRA, allowing for expedited clinical application as phase II trials for children with high-risk PFA.

A Multimodal Intervention to Reduce C. difficile Infections and Stool Testing

BACKGROUND AND OBJECTIVES

The introduction of multiplex gastrointestinal panels at our institution resulted in increased Clostridioides difficile (C. difficile) detection and stool test utilization. We aimed to reduce hospital-onset C. difficile infections (HO-CDIs), C. difficile detection, and overall stool testing by 20% within 1 year.

METHODS

We conducted a quality improvement project from 2018 to 2020 at a large children's hospital. Interventions included development of a C. difficile testing and treatment clinical care pathway, new options for gastrointestinal panel testing with or without C. difficile (results were suppressed if not ordered), clinical decision support tool to restrict testing, and targeted prevention efforts. Outcomes included the rate of HO-CDI (primary), C. difficile detection, and overall stool testing. All measures were evaluated monthly among hospitalized children per 10 000 patient-days (PDs) using statistical process-control charts. For balancing measures, we tracked suppressed C. difficile results that were released during real-time monitoring because of concern for true infection and C. difficile-related adverse events.

RESULTS

HO-CDI decreased by 55%, from 11 to 5 per 10 000 PDs. C. difficile detection decreased by 44%, from 18 to 10 per 10 000 PDs, and overall test utilization decreased by 29%, from 99 to 70 per 10 000 PDs. The decrease in stool tests resulted in annual savings of $55 649. Only 2.3% of initially suppressed positive C. difficile results were released, and no patients had adverse events.

CONCLUSIONS

Diagnostic stewardship strategies, coupled with an evidence-based clinical care pathway, can be used to decrease C. difficile and improve overall test utilization.

Indoximod-based chemo-immunotherapy for pediatric brain tumors: A first-in-children phase I trial

BACKGROUND

Recurrent brain tumors are the leading cause of cancer death in children. Indoleamine 2,3-dioxygenase (IDO) is a targetable metabolic checkpoint that, in preclinical models, inhibits anti-tumor immunity following chemotherapy.

METHODS

We conducted a phase I trial (NCT02502708) of the oral IDO-pathway inhibitor indoximod in children with recurrent brain tumors or newly diagnosed diffuse intrinsic pontine glioma (DIPG). Separate dose-finding arms were performed for indoximod in combination with oral temozolomide (200 mg/m2/day x 5 days in 28-day cycles), or with palliative conformal radiation. Blood samples were collected at baseline and monthly for single-cell RNA-sequencing with paired single-cell T cell receptor sequencing.

RESULTS

Eighty-one patients were treated with indoximod-based combination therapy. Median follow-up was 52 months (range 39-77 months). Maximum tolerated dose was not reached, and the pediatric dose of indoximod was determined as 19.2 mg/kg/dose, twice daily. Median overall survival was 13.3 months (n = 68, range 0.2-62.7) for all patients with recurrent disease and 14.4 months (n = 13, range 4.7-29.7) for DIPG. The subset of n = 26 patients who showed evidence of objective response (even a partial or mixed response) had over 3-fold longer median OS (25.2 months, range 5.4-61.9, p = 0.006) compared to n = 37 nonresponders (7.3 months, range 0.2-62.7). Four patients remain free of active disease longer than 36 months. Single-cell sequencing confirmed emergence of new circulating CD8 T cell clonotypes with late effector phenotype.

CONCLUSIONS

Indoximod was well tolerated and could be safely combined with chemotherapy and radiation. Encouraging preliminary evidence of efficacy supports advancing to Phase II/III trials for pediatric brain tumors.

Pediatric pineal region masses: a single-center experience over 25 years

PURPOSE

Pineal region tumors (PRT) represent less than 1% of brain neoplasms. The rare and heterogeneous nature of these tumors is reflected in the variety of treatment modalities employed.

METHODS

A single-center retrospective review of all pediatric patients with pineal region tumors between November 1996 and June 2021 was performed. Fifty-six cases of pineal tumors were reviewed for age and symptoms upon presentation, diagnostic methods, imaging characteristics, histological classification, treatment modalities, recurrence, and mortality rates.

RESULTS

The average age at diagnosis was 11.3 years. The majority of patients were male (82.1%) and Caucasian (73.2%). The most common presenting symptoms were headache (n = 38, 67.9%) and visual problems (n = 34, 60.7%). Hydrocephalus was present in 49 patients (87.5%). Germinoma (n = 20, 35.7%) and non-germinomatous germ cell tumor (NGGCT) (n = 17, 30.4%) were the most common tumors. Chemotherapy was employed for 54 patients (96.4%), radiation for 49 (87.5%), and surgical resection for 14 (25.0%). The average duration of treatment was 5.9 months. Progression-free survival was 74.4% at 5 years and 72.0% at 10 years. Overall survival was 85.7% at 5 years and 77.1% at 10 years.

CONCLUSION

Treatment of pineal region tumors must be targeted to each patient based on presentation, subtype, presence of hydrocephalus, and extent of disease. Upfront surgical resection is usually not indicated. As advances in oncological care proceed, treatment modalities may continue to improve in efficacy.

Outcomes of Infants and Young Children With Relapsed Medulloblastoma After Initial Craniospinal Irradiation-Sparing Approaches: An International Cohort Study

PURPOSE

Infant and young childhood medulloblastoma (iMB) is usually treated without craniospinal irradiation (CSI) to avoid neurocognitive late effects. Unfortunately, many children relapse. The purpose of this study was to assess salvage strategies and prognostic features of patients with iMB who relapse after CSI-sparing therapy.

METHODS

We assembled a large international cohort of 380 patients with relapsed iMB, age younger than 6 years, and initially treated without CSI. Univariable and multivariable Cox models of postrelapse survival (PRS) were conducted for those treated with curative intent using propensity score analyses to account for confounding factors.

RESULTS

The 3-year PRS, for 294 patients treated with curative intent, was 52.4% (95% CI, 46.4 to 58.3) with a median time to relapse from diagnosis of 11 months. Molecular subgrouping was available for 150 patients treated with curative intent, and 3-year PRS for sonic hedgehog (SHH), group 4, and group 3 were 60%, 84%, and 18% (P = .0187), respectively. In multivariable analysis, localized relapse (P = .0073), SHH molecular subgroup (P = .0103), CSI use after relapse (P = .0161), and age ≥ 36 months at initial diagnosis (P = .0494) were associated with improved survival. Most patients (73%) received salvage CSI, and although salvage chemotherapy was not significant in multivariable analysis, its use might be beneficial for a subset of children receiving salvage CSI < 35 Gy (P = .007).

CONCLUSION

A substantial proportion of patients with relapsed iMB are salvaged after initial CSI-sparing approaches. Patients with SHH subgroup, localized relapse, older age at initial diagnosis, and those receiving salvage CSI show improved PRS. Future prospective studies should investigate optimal CSI doses and the role of salvage chemotherapy in this population.

Therapeutic targeting of prenatal pontine ID1 signaling in diffuse midline glioma

BACKGROUND

Diffuse midline gliomas (DMG) are highly invasive brain tumors with rare survival beyond two years past diagnosis and limited understanding of the mechanism behind tumor invasion. Previous reports demonstrate upregulation of the protein ID1 with H3K27M and ACVR1 mutations in DMG, but this has not been confirmed in human tumors or therapeutically targeted.

METHODS

Whole exome, RNA, and ChIP-sequencing was performed on the ID1 locus in DMG tissue. Scratch-assay migration and transwell invasion assays of cultured cells were performed following shRNA-mediated ID1-knockdown. In vitro and in vivo genetic and pharmacologic [cannabidiol (CBD)] inhibition of ID1 on DMG tumor growth was assessed. Patient-reported CBD dosing information was collected.

RESULTS

Increased ID1 expression in human DMG and in utero electroporation (IUE) murine tumors is associated with H3K27M mutation and brainstem location. ChIP-sequencing indicates ID1 regulatory regions are epigenetically active in human H3K27M-DMG tumors and prenatal pontine cells. Higher ID1-expressing astrocyte-like DMG cells share a transcriptional program with oligo/astrocyte-precursor cells (OAPCs) from the developing human brain and demonstrate upregulation of the migration regulatory protein SPARCL1. Genetic and pharmacologic (CBD) suppression of ID1 decreases tumor cell invasion/migration and tumor growth in H3.3/H3.1K27M PPK-IUE and human DIPGXIIIP* in vivo models of pHGG. The effect of CBD on cell proliferation appears to be non-ID1 mediated. Finally, we collected patient-reported CBD treatment data, finding that a clinical trial to standardize dosing may be beneficial.

CONCLUSIONS

H3K27M-mediated re-activation of ID1 in DMG results in a SPARCL1+ migratory transcriptional program that is therapeutically targetable with CBD.

A novel preclinical model of craniospinal irradiation in pediatric diffuse midline glioma demonstrates decreased metastatic disease

Background

Diffuse midline glioma (DMG) is an aggressive pediatric central nervous system tumor with strong metastatic potential. As localized treatment of the primary tumor improves, metastatic disease is becoming a more important factor in treatment. We hypothesized that we could model craniospinal irradiation (CSI) through a DMG patient-derived xenograft (PDX) model and that CSI would limit metastatic tumor.

Methods

We used a BT245 murine orthotopic DMG PDX model for this work. We developed a protocol and specialized platform to deliver craniospinal irradiation (CSI) (4 Gy x2 days) with a pontine boost (4 Gy x2 days) and compared metastatic disease by pathology, bioluminescence, and MRI to mice treated with focal radiation only (4 Gy x4 days) or no radiation.

Results

Mice receiving CSI plus boost showed minimal spinal and brain leptomeningeal metastatic disease by bioluminescence, MRI, and pathology compared to mice receiving radiation to the pons only or no radiation.

Conclusion

In a DMG PDX model, CSI+boost minimizes tumor dissemination compared to focal radiation. By expanding effective DMG treatment to the entire neuraxis, CSI has potential as a key component to combination, multimodality treatment for DMG designed to achieve long-term survival once novel therapies definitively demonstrate improved local control.

Pediatric Central Nervous System Cancers, Version 2.2023, NCCN Clinical Practice Guidelines in Oncology

Central nervous system (CNS) cancers account for approximately one quarter of all pediatric tumors and are the leading cause of cancer-related death in children. More than 4,000 brain and CNS tumors are diagnosed each year in children and teens, and the incidence rate has remained stagnant in recent years. The most common malignant pediatric CNS tumors are gliomas, embryonal tumors consisting of predominately medulloblastomas, and germ cell tumors. The inaugural version of the NCCN Guidelines for Pediatric Central Nervous System Cancers focuses on the diagnosis and management of patients with pediatric diffuse high-grade gliomas. The information contained in the NCCN Guidelines is designed to help clinicians navigate the complex management of pediatric patients with diffuse high-grade gliomas. The prognosis for these highly aggressive tumors is generally poor, with 5-year survival rates of <20% despite the use of combined modality therapies of surgery, radiation therapy and systemic therapy. Recent advances in molecular profiling has expanded the use of targeted therapies in patients whose tumors harbor certain alterations. However, enrollment in a clinical trial is the preferred treatment for eligible patients.

CSIG-09. THERAPEUTIC TARGETING OF PRENATAL PONTINE ID1 SIGNALING IN DIFFUSE MIDLINE GLIOMA

Diffuse midline gliomas (DMG) are highly invasive brain tumors with rare survival beyond two years past diagnosis. The mechanism behind tumor invasion is currently not well understood. Previous reports demonstrate upregulation of the protein ID1 with H3K27M and ACVR1 mutations in DMG, but this has not been confirmed in human tumors or therapeutically targeted. Whole exome, RNA, and ChIP-sequencing were performed on the ID1 locus in DMG tissue. Scratch-assay migration and transwell invasion assays of cultured cells were performed following shRNA-mediated ID1-knockdown. In vitro and in vivo genetic and pharmacologic [cannabidiol (CBD)] inhibition of ID1 on DMG tumor growth was assessed. Additional in vitro experiments were performed to determine a potential mechanism of action for CBD-mediated effects. Self-reported CBD dosing information was collected from DMG patients. We found that increased ID1 expression in human DMG and in utero electroporation (IUE) murine tumors is associated with H3K27M mutation and brainstem location. ChIP-sequencing indicates a similar epigenetically active state at ID1 regulatory regions in human H3K27M-DMG tumors and prenatal pontine cells. Higher ID1-expressing astrocyte-like DMG cells share a transcriptional program with oligo/astrocyte-precursor cells (OAPCs) from the developing human brain and demonstrate upregulation of the migration regulatory protein SPARCL1. Genetic and pharmacologic (CBD) suppression of ID1 decreases tumor cell migration, tumor growth, and to a lesser extent invasion in both murine IUE and multiple patient-derived in vivo DMG models, improving mouse survival. ID1 knockdown significantly decreases the effect of CBD on migration, tumor growth, and invasion. CBD increases reactive oxygen species production, which also affects DMG cell proliferation in a non-ID1 mediated manner. Overall, we find that H3K27M-mediated reactivation of ID1 in DMG results in a SPARCL1+ migratory transcriptional program that is therapeutically targetable with CBD.

CTIM-32. FIRST-IN-CHILDREN PHASE 1 TRIAL OF INDOXIMOD-BASED CHEMO-IMMUNOTHERAPY FOR PATIENTS WITH PEDIATRIC BRAIN TUMORS: ANALYSIS OF SAFETY, TOLERABILITY, AND 5-YEAR OUTCOME

BACKGROUND

Recurrent brain tumors are the leading cause of cancer death in children. We conducted a first-in-children, two-institution, Phase 1 open-label dose-confirmation study using a 3 + 3 design, with expansion cohorts, to determine the recommended pediatric dose of the IDO pathway-inhibitor indoximod (NCT02502708). DESIGN/

METHODS

Eligible patients were 3-22 years old with either recurrent malignant brain tumor or newly-diagnosed diffuse intrinsic pontine glioma (DIPG). Palliative radiation, surgery or dexamethasone were allowed as needed for patient management. Separate dose-finding arms were performed for indoximod plus temozolomide (200 mg/m2/day orally for 5 days of each 28-day cycle) and for indoximod plus conformal radiation (in patients for whom re-irradiation was planned as standard-of-care). At progression, patients who were otherwise clinically stable were offered crossover to indoximod plus a second-line chemotherapy regimen (cyclophosphamide 2.5 mg/kg/day orally and etoposide 50 mg/m2/day orally for 21 days of each 28-day cycle).

RESULTS

Between December 2015 and January 2019, the study enrolled 81 brain tumor patients, including newly-diagnosed DIPG (n = 13) or recurrent ependymoma (n = 27), glioblastoma/high-grade glioma (n = 19), medulloblastoma (n = 13), or other CNS tumors ( n= 9). Median follow-up was 52 months (range 39-77 months). No dose-limiting toxicities were observed, and the pediatric indoximod dose was determined (19.2 mg/kg/dose, given twice daily). Indoximod was well tolerated and did not affect the ability to deliver chemotherapy or radiation as planned. Median overall survival was 13.6 months (n = 81). Median overall survival was 34.7 months for the subset of patients who continued indoximod with second-line chemotherapy after progression on indoximod plus temozolomide (n = 18).

CONCLUSIONS

Indoximod was well tolerated and could be combined with a variety of standard treatments for pediatric brain tumors. Preliminary anti-tumor activity and overall survival suggest that indoximod with standard therapy should be further evaluated in pediatric brain tumors, and potentially other pediatric solid tumors.

BIOM-49. A PILOT STUDY OF CEREBROSPINAL FLUID EXOSOMAL SMALL RNA-SEQUENCING IN PEDIATRIC MEDULLOBLASTOMA PATIENTS ON THE NEXT CONSORTIUM “HEAD START” 4 PROTOCOL

BACKGROUND

Head Start 4 is a randomized clinical trial to determine whether dose-intensive tandem consolidation, compared with a single cycle, with autologous hematopoietic progenitor cell rescue provides a survival benefit in pediatric patients with medulloblastoma or other embryonal tumors. The trial incorporates upfront molecular subgrouping and non-mandatory, prospective blood and cerebrospinal fluid (CSF) collection. This pilot study aimed to identify exosomal non-coding RNAs (exo-ncRNAs) that might serve as novel diagnostic and/or treatment response biomarkers.

METHODS

CSF(1-2mLs) from 11 controls (non-tumor) and 27 medulloblastoma participants including 23 obtained at baseline, 22 at the end of induction, 3 post-consolidation, and 4 relapse time points, were profiled. Exosome isolation and small RNA-sequencing were performed by System Biosciences. Differential gene expression (DGE) was performed in R (DESeq2). Variations in gene expression profiles between samples were visualized using principal component analysis.

RESULTS

After limiting to ncRNAs with expression of 2 counts per million in 50% or more of the samples in each comparison, ~9,500 ncRNAs were detected. DGE analyses revealed 118 ncRNAs with log2 fold change(FC) &gt;2 and 1 ncRNA with log2FC&lt; -2 in baseline CSF samples compared to controls. In contrast, 11 ncRNAs(log2FC &gt;2) and 1 ncRNA(log2FC&lt; -2) were detected in end of induction CSF samples compared to controls. Comparing end of induction to baseline CSF samples accounting for paired samples, 0 ncRNAs(log2FC &gt;2) and 52 ncRNAs(log2FC&lt; -2) were detected.

CONCLUSIONS

Overall, our data indicate that exosomal small RNA-sequencing of limited CSF volumes is feasible. Differential expression and distinct clustering between tumor baseline samples compared to non-tumor controls was observed. CSF-derived exo-ncRNAs at end of induction also demonstrated “normalization” of ncRNA profiles, signifying CSF biomarkers may serve a role in diagnosis and molecular response assessment. A comprehensive analysis including multi-marker predictive model development and molecular subgrouping will be undertaken at completion of study enrollment.

Novel clinical algorithm for hypothalamic obesity in youth with brain tumours and factors associated with excess weight gain

BACKGROUND

A standardized approach for identifying and treating hypothalamic obesity (HO) in children with hypothalamic tumours is lacking.

OBJECTIVES

To describe children with hypothalamic tumours at risk for obesity, assess outcomes of a novel HO clinical algorithm, and identify factors associated with weight gain.

METHODS

Retrospective analysis of youth with hypothalamic and suprasellar tumours, seen at a paediatric tertiary care centre from 2010 to 2020.

RESULTS

The study cohort (n = 130, 50% female, median age at diagnosis 5 [range 0-17]y) had a median duration of follow up of 5 (0.03-17)y. At last recorded body mass index (BMI) measurement, 34% had obesity, including 17% with severe obesity. Median onset of overweight and obesity after diagnosis was 6.2 (0.3-134) and 8.9 (0.7-65) months, respectively. After algorithm implementation (n = 13), the proportion that had an early dietitian visit (within 6 months) increased from 36% to 54%, (p = 0.498) and weight management referrals increased from 51% to 83% (p = 0.286). Higher BMI z-score at diagnosis was associated with overweight and obesity development (p < 0.001).

CONCLUSION

Patients with hypothalamic tumours commonly develop obesity. Use of a clinical algorithm may expedite recognition of HO. Further research is needed to identify predictors of weight gain and to develop effective treatment.

LTBK-04. LATE BREAKING ABSTRACT: MEK162 (binimetinib) in children with progressive or recurrent low-grade glioma: a multi-institutional phase II and target validation study

BACKGROUND

RAS/RAF/MEK/ERK pathway activation is the primary driver for most pediatric low-grade gliomas (pLGG). MEK162 (binimetinib) is an orally bioavailable MEK1/2 inhibitor with superior brain penetration in a preclinical model. The primary objective of this multi-institutional phase II and target validation study was to assess stratum-specific efficacy of binimetinib in progressive pLGG.

METHODS

Eligible children aged 1-18 years with previously treated radiographically progressive pLGG were enrolled and treated with binimetinib, starting dose 32mg/m2/dose twice daily. Stratum 1 included patients with pLGG with documented BRAF fusion; stratum 2, neurofibromatosis 1 (NF1)-associated pLGG; stratum 3, sporadic pLGG without documented BRAF fusion; and stratum 4, patients undergoing planned tumor biopsy who began binimetinib preoperatively. Partial and minor responses (PR and MR) were defined as ≥50% and ≥25% decrease in maximal two-dimensional measurements.

RESULTS

Of 86 patients enrolled, 85 were evaluable for response. Of these, 48 (56%) showed a radiographic response (30 PR and 18 MR) in the first year of treatment. Response rate for stratum 1 (n=28) was 50% (12 PR and 2 MR); 12 (43%) had stable disease (SD) and 2 (7%) progressive disease (PD). Stratum 2 (n=21) response rate was 43% (5 PR, 4 MR), with 12 (57%) SD and no PD. Stratum 3 (n=29) response rate was 69% (10 PR, 10 MR), 4 (14%) SD and 5 (17%) PD. Stratum 4 (n=7) include 3 PR, 2 MR, 2 SD. Nineteen (22%) discontinued treatment for toxicity (most commonly dermatologic), and an additional 42 (49%) required dose reduction. Median dose at the time of PR/MR was 28mg/m2; responses were seen at doses as low 16mg/m2.

CONCLUSION

Binimetinib is highly effective in the treatment of both NF1-associated and sporadic pLGG, with or without documented BRAF fusion. Modified dosing strategies to improve tolerability may be considered in future trials.

RARE-32. Phase 0 and feasibility single-institution clinical trial of intravenous tocilizumab for adamantinomatous craniopharyngioma

BACKGROUND: Adamantinomatous craniopharyngioma (ACP) is a devastating skull-base tumor believed to derive from epithelial remnants of the primordial craniopharyngeal duct (Rathke’s pouch), which gives rise to the anterior pituitary gland. ACP lacks medical antitumor therapies. Current standard therapy with surgery and radiation is associated with poor quality of life. Clinical and preclinical data indicate that IL-6 blockade may contribute to ACP tumor control. METHODS: Children aged 2–21 years with newly diagnosed or previously treated ACP with measurable disease are eligible for the Phase 0/feasibility single-institution clinical trial (NCT03970226) of intravenous (IV) tocilizumab at Children’s Hospital Colorado. The phase I stratum involves IV tocilizumab prior to a standard-of-care surgical resection. The feasibility portion of the trial involves IV tocilizumab every two weeks for up to 13 28-day cycles. Tocilizumab is administered at the established weight-based pediatric dosage of 8 mg/kg for patients who weigh ≥30kg or 12 mg/kg for patients who weigh <30kg. RESULTS: To date, three patients have been enrolled on the Phase 0 component of the trial. These patients demonstrated clinically relevant levels of tocilizumab (≥ 4µg/mL) in serum, cyst fluid, and/or tumor tissue, compared to undetectable levels in control samples. Two patients (1 male and 1 female; median age 10.5 years) have enrolled on the feasibility stratum; one patient had best response of minor response but met definition of progressive disease at cycle 11. One patient with extensive disease required dose reduction for myelosuppression. CONCLUSION: Systemic delivery of tocilizumab at the established pediatric dosage is promising for treatment of ACP based on preclinical work and its demonstrated penetration into cystic and solid portions of ACP tumors. The therapy to date has been well tolerated overall. Further study is planned through a CONNECT consortium international Phase II trial.

EPEN-30. 5FU with Radiation Followed by Maintenance of 5FU and ATRA Significantly Improves Survival of 1q+/6q- PFA Ependymoma Xenograft Models

In a screen of over 100 FDA approved drugs on PFA 1q+ EPN cells, 5-fluorouracil (5FU) and All-Trans-Retinoic Acid (ATRA) were identified as inhibitors of EPN cell line growth. We performed in-vitro cell growth assays combining increasing doses of radiation and 5FU and found a significant synergistic effect on cell growth and apoptosis in 1q+ PFA EPN cell lines. Further growth attenuation was seen when ATRA was added 48 hours following radiation and 5FU treatment. This led us to development of preclinical studies in the 1q+ PFA orthotopic xenograft models MAF-811_XF and MAF-928_XF. In the initial cohort, tumors were allowed to establish prior to treatment start confirmed by MRI. In both MAF-811 and MAF-928, chemotherapy improved survival compared to no treatment. As consistent with standard of care, radiation significantly improved survival (p=0.0016) but there was no added benefit to combining 5FU or 5FU+ATRA with radiation. A second cohort was treated using the same treatment approach, however radiation and 5FU were started with minimal to no visible tumors by MRI. Interestingly, we found a significant increase in survival between vehicle control and combination 5FU+ATRA (HR 5.121, 95% CI: 0.2506, 2.409, p=0.048) in MAF-811 mice. However, again with radiation, there was no significant change in survival with only a single cycle of 5FU+ATRA. This led to continued maintenance of 5FU+ATRA cycles of 6 weeks with 2 weeks off for 4 cycles post radiation in mice with minimal tumor. When 5FU with radiation is followed by 5FU+ATRA and is continued in mice with minimal disease, survival significantly improved when compared to radiation alone (HR 9.020, 95% CI: 1.933 to 42.09, p=0.007). These studies highlight the importance of chemotherapy in minimal disease and is the rationale for a Phase I/II study in relapsed PFA EPN and in upfront 1q+ PFA EPN.

DIPG-25. Patterns of cerebrospinal fluid diversion and survival in children with diffuse intrinsic pontine glioma: a report from the International Diffuse Intrinsic Pontine Glioma Registry

BACKGROUND: There are no standard practice guidelines for cerebrospinal (CSF) diversion for diffuse intrinsic pontine glioma (DIPG), nor clear understanding of potential for palliation and life-prolongation. We evaluated CSF diversion characteristics in children with DIPG to determine incidence, indications, symptom effects, and survival. METHODS: Data were extracted from subjects registered in the International DIPG registry (IDIPGR). Univariable analyses was performed using the Fisher’s exact test or Wilcoxon rank sum test. Survival was estimated using the Kaplan-Meier method. RESULTS: Evaluable patients (n=542) met criteria for DIPG diagnosis by central radiologic review; of those, 126 (23%) had permanent CSF diversion. Median time from diagnosis to diversion was 0.5 months (IQR 0.1-4.5 months). Those with permanent diversion were significantly younger (median 5.4 years vs 7.0 years, p<0.001) and had higher incidence of hydrocephalus at diagnosis (65.3% vs 11.9%, p<0.001). Permanent CSF diversion did not significantly impact overall survival (OS) (p=0.4), even amongst the 124 patients with hydrocephalus at presentation (p=0.20). Those with permanent diversion prior to radiation therapy demonstrated longer median OS than those in whom diversion was placed after radiation (14.3 vs 9.6 months, p=0.001). Patients reported significantly less headache and vomiting at last follow up after permanent CSF diversion compared to pre-diversion (p<0.0001 and p=0.001, respectively), however steroid use was also significantly higher at last follow-up after CSF diversion (p<0.001). CONCLUSIONS: Amongst an international cohort, DIPG patients who had permanent CSF diversion were significantly younger and had higher rates of hydrocephalus at initial presentation than those without permanent diversion. Symptoms of increased intracranial pressure improved in those with CSF diversion, although a direct effect may be confounded by increased steroid use. Permanent CSF diversion did not prolong overall survival in this large cohort of patients, even amongst those who presented with hydrocephalus.

EPCT-01. Pediatric Brain Tumor Consortium (PBTC)-055: A phase I study of trametinib and hydroxychloroquine (HCQ) for BRAF-fusion or Neurofibromatosis type-1 (NF1)-associated pediatric gliomas

INTRODUCTION: Autophagy is a highly conserved process by which intracellular components are degraded and recycled promoting cell survival. Preclinically, autophagy has been implicated as a resistance mechanism in BRAF-mutant glioma cells treated with MAPK-pathway inhibitors. HCQ, an oral autophagy inhibitor, has been evaluated preclinically and clinically to overcome resistance. METHODS: PBTC-055 (NCT04201457) is a phase I/II trial of HCQ combined with trametinib (BRAF-fusion or NF1-associated gliomas) or trametinib and dabrafenib (BRAFV600E gliomas) in patients &lt; 30 years with progressive glioma. Prior treatment with RAF and/or MEK inhibitor with sub-optimal response (no response or response followed by progression on therapy) was required. Here, we present phase I data combining trametinib with HCQ utilizing a rolling-6 design. HCQ was administered at escalating dose levels (8, 15, or 20 mg/kg/day divided BID) in combination with standard pediatric trametinib dosing. All patients received prior MEK inhibitor therapy; 5/18 (28%) exhibited no response and 13/18 (72%) progressed on active therapy. RESULTS: Eighteen eligible/evaluable subjects were enrolled. Median age was 9.6 years (2.5-20.4 years); 10 were male. There were 2 dose-limiting toxicities (both grade 3 rash one each at DL1 and DL3). The highest dose level of HCQ (20 mg/kg/day divided BID) was declared the RP2D. Grade 3 adverse events possibly related to therapy included skin infection, rash, cardiac ejection fraction decrease, weight loss, and anorexia. There were no grade 4 or 5 attributable toxicities. Preliminarily, combination pharmacokinetic assessment revealed similar metabolism of trametinib to that reported as a single agent; HCQ demonstrated more rapid clearance compared to adults. Pharmacodynamic assessments are ongoing. CONCLUSIONS: The combination of trametinib and HCQ is safe with a RP2D of HCQ of 20 mg/kg/day divided BID. Currently, subjects are enrolling on the phase II portion evaluating the efficacy of this novel combination.

RONC-05. Peri-transplant Radiation Therapy for Young Children Treated with High-Dose Chemotherapy for Primary Brain Tumors

PURPOSE: The role of peri-transplant radiation therapy (RT) in young children with primary brain tumors is unclear. We characterized our institutional practice patterns and patient outcomes. MATERIALS AND METHODS: The cohort included all patients treated with high-dose chemotherapy for primary brain tumors at our institution from 2011-2017. Rates of local control (LC), progression-free survival (PFS), overall survival (OS), and radiation-associated injury were assessed. RESULTS: Of 37 eligible patients, 29 (78%) received peri-transplant RT at a median age of 4 years. Patients treated with RT were more likely to have metastatic (p=0.0121) and incompletely resected (p=0.056) disease, and to have high-risk histologies including atypical teratoid rhabdoid tumor, nongerminomatous germ cell tumor, pineoblastoma, primitive neuro-ectodermal tumor, glioneuronal tumor and group 3 medulloblastoma. Of those treated with RT, 13 (45%) received craniospinal irradiation (CSI) and 16 (55%) received focal RT. The median CSI dose was 23.4 Gy (IQR: 18-36; boost median 54 Gy [IQR: 53.7-55.8]) and focal RT dose was 50.4 Gy (IQR: 50.4-54.5). Compared to the focal RT group, patients treated with CSI were older (p=0.0499) and more likely to have metastatic disease (p=0.0004). For the complete cohort, at a median follow-up of 3.8 years, the 2-year rate of LC was 82% (95% CI: 70-96%), PFS was 63% (95% CI: 49-81%), and OS was 65% (95% CI: 51-82%). These rates did not differ significantly between patients treated with and without peri-transplant RT. Two cases of fatal myelopathy were observed after spinal cord doses within the highest tertile (41.4 CGE and 36 Gy); both cases occurred in patients who received RT before high-dose chemotherapy. CONCLUSION: Peri-transplant RT was used for high-risk disease. Oncologic outcomes after RT were encouraging. However, 2 cases of grade 5 myelopathy were observed. If used cautiously, RT may contribute to durable remission in patients at high risk of relapse.

EPEN-11. Phase 0/I Study of GM-CSF and Intrathecal Trastuzumab In Children With Recurrent Posterior Fossa Ependymoma

BACKGROUND: Posterior fossa ependymoma (PF EPN) is a pediatric central nervous system malignancy that has a poor outcome to standard therapeutic approaches. The majority of PF EPN have been shown to harbor increased HER2 expression, making it a logical therapeutic target. Trastuzumab is a monoclonal antibody that targets HER2, and sargramostim (GM-CSF) stimulates hematopoietic progenitor cell proliferation. The combination of trastuzumab and GM-CSF has been shown to trigger antibody-dependent cell cytotoxicity in-vitro in patient-derived PF EPN cell lines. METHODS: Children aged 1–21 years with relapsed PF EPN, no ventriculoperitoneal shunt, and no CSF obstruction are eligible for the Phase 0/I single-institution clinical trial at Children’s Hospital Colorado. Stratum 1 involves intrathecal (IT) trastuzumab and subcutaneous (subQ) GM-CSF prior to standard-of-care surgical resection. Stratum 2 involves a 3 + 3 phase I design with serial IT trastuzumab doses, each preceded by three days of GM-CSF, to establish the maximum tolerated dose for IT trastuzumab. RESULTS: Trastuzumab was detected in a sufficient number of tumors after presurgical IT delivery in Stratum 1 to open Stratum 2. Seven patients (3 female) have been enrolled in Stratum 2. Median age at enrollment is 8.1 years (range, 3–20 years). CSF pharmacokinetic analysis demonstrate detectable trastuzumab up to 14 days after IT doses. No dose-limiting toxicities or grade 3 or 4 adverse events have occurred. Four patients completed all planned study therapy and remain progression-free post-therapy (median, 23 months, range, 6-42 months). Three patients progressed on therapy (median, 4 cycles). Biologic correlative studies are in process. CONCLUSIONS: IT trastuzumab penetrates PF EPN tumor tissue and demonstrates an excellent safety profile. Stratum 2 remains open to accrual at Dose Level 2. IT trastuzumab+GM-CSF warrants consideration for a multi-institutional Phase II trial.

SWK-10. Survivorship: Education, Clinical Guidelines, and Transition to Adult Care

As the cure rates of patients with pediatric brain tumors increases, the long term care needs of the survivors increase as well. Survivorship includes several facets of multidisciplinary care including education, clinical care guidelines, and transition to adult medical care. The neuro-oncology program at a large tertiary care hospital has developed a team to address survivorship needs. The Children’s Oncology Group (COG) Long-Term Follow-Up Guidelines for Survivors of Childhood, Adolescent, and Young Adult Cancers was utilized as a backbone that was then customized for neuro-oncology patient education including disease type and treatment. The education was compiled into patient handouts as well as electronic medical record (EMR) statements that can easily be added to a clinic note or letter to referring providers. In addition, a diagnosis and treatment summary was placed both in the EMR as well as given to patients at various time points to ensure long term knowledge. Next, follow-up guidelines and roadmaps were developed and customized to tumor type and treatment received (surgery, radiation, chemotherapy). The roadmaps ensure patients are receiving high-quality comprehensive follow-up and screening from a large multidisciplinary team. Finally, patients will transition to adult care. With a large seven state catchment area, the adult care providers vary on local provider availability, knowledge, and medical complexity of the survivor. Each patient is evaluated based on their needs, availability of care locally, and ability to travel. The team developed relationships with the clinical team at the academic center adjacent to the pediatric hospital to support a smooth transition to adult care. The adult neuro-oncology care team can also serve as a consulting service for local adult providers. The survivorship team will continue to address the complex needs of brain tumor survivors and provide education for a smooth transition to adult care.

Characteristics of children ≤36 months of age with DIPG: A report from the international DIPG registry

BACKGROUND

Children ≤36 months with diffuse intrinsic pontine glioma (DIPG) have increased long-term survival (LTS, overall survival (OS) ≥24 months). Understanding distinguishing characteristics in this population is critical to improving outcomes.

METHODS

Patients ≤36 months at diagnosis enrolled on the International DIPG Registry (IDIPGR) with central imaging confirmation were included. Presentation, clinical course, imaging, pathology and molecular findings were analyzed.

RESULTS

Among 1183 patients in IDIPGR, 40 were eligible (median age: 29 months). Median OS was 15 months. Twelve patients (30%) were LTS, 3 (7.5%) very long-term survivors ≥5 years. Among 8 untreated patients, median OS was 2 months. Patients enrolled in the registry but excluded from our study by central radiology review or tissue diagnosis had median OS of 7 months. All but 1 LTS received radiation. Among 32 treated patients, 1-, 2-, 3-, and 5-year OS rates were 68.8%, 31.2%, 15.6% and 12.5%, respectively. LTS had longer duration of presenting symptoms (P = .018). No imaging features were predictive of outcome. Tissue and genomic data were available in 18 (45%) and 10 patients, respectively. Among 9 with known H3K27M status, 6 had a mutation.

CONCLUSIONS

Children ≤36 months demonstrated significantly more LTS, with an improved median OS of 15 months; 92% of LTS received radiation. Median OS in untreated children was 2 months, compared to 17 months for treated children. LTS had longer duration of symptoms. Excluded patients demonstrated a lower OS, contradicting the hypothesis that children ≤36 months with DIPG show improved outcomes due to misdiagnosis.

Accuracy of central neuro-imaging review of DIPG compared with histopathology in the International DIPG Registry

BACKGROUND

Diffuse intrinsic pontine glioma (DIPG) remains a clinico-radiologic diagnosis without routine tissue acquisition. Reliable imaging distinction between DIPG and other pontine tumors with potentially more favorable prognoses and treatment considerations is essential.

METHODS

Cases submitted to the International DIPG registry (IDIPGR) with histopathologic and/or radiologic data were analyzed. Central imaging review was performed on diagnostic brain MRIs (if available) by two neuro-radiologists. Imaging features suggestive of alternative diagnoses included nonpontine origin, <50% pontine involvement, focally exophytic morphology, sharply defined margins, and/or marked diffusion restriction throughout.

RESULTS

Among 286 patients with pathology from biopsy and/or autopsy, 23 (8%) had histologic diagnoses inconsistent with DIPG, most commonly nondiffuse low-grade gliomas and embryonal tumors. Among 569 patients with centrally-reviewed diagnostic MRIs, 40 (7%) were classified as non-DIPG, alternative diagnosis suspected. The combined analysis included 151 patients with both histopathology and centrally-reviewed MRI. Of 77 patients with imaging classified as characteristic of DIPG, 76 (99%) had histopathologic diagnoses consistent with DIPG (infiltrating grade II-IV gliomas). Of 57 patients classified as likely DIPG with some unusual imaging features, 55 (96%) had histopathologic diagnoses consistent with DIPG. Of 17 patients with imaging features suggestive of an alternative diagnosis, eight (47%) had histopathologic diagnoses inconsistent with DIPG (remaining patients were excluded due to nonpontine tumor origin). Association between central neuro-imaging review impression and histopathology was significant (p < 0.001), and central neuro-imaging impression was prognostic of overall survival.

CONCLUSIONS

The accuracy and important role of central neuro-imaging review in confirming the diagnosis of DIPG is demonstrated.

TAMI-79. THERAPEUTIC REVERSAL OF PRENATAL PONTINE ID1 SIGNALING IN DIPG

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brain tumor with rare survival beyond two years. This poor prognosis is largely due to the tumor's highly infiltrative and invasive nature. Nearly 80% of DMGs harbor K27M mutation in the genes encoding histone H3.1 (H3F3A) or H3.3 (HISTIH3B), often with concurrent ACVR1 mutation. Inhibitor of DNA-binding (ID) proteins are key transcriptional regulators of genes involved in lineage commitment and are associated with invasiveness and poor clinical outcomes in multiple human cancers. Introduction of H3K27M and ACVR1 mutations increase ID1 expression in cultured astrocytes, but this has not been confirmed in human tumors or targeted therapeutically. We developed an in-utero electroporation (IUE) murine H3K27M-driven tumor model, which demonstrates increased ID1 expression in H3K27M- and ACVR1-mutated tumor cells. Exome and transcriptome sequencing analysis of multi-focal DMG tumors (n=52) and normal brain tissue revealed that increased ID1 expression is associated with H3K27M/ACVR1-mutation and brainstem location, and correlates with poor survival in patients. ChIP-sequencing for H3K27ac and H3K27me3 in multiple DMG tumors (n=5) revealed that the ID1 gene is epigenetically active, which matches the epigenetic state of murine prenatal hindbrain cells. Higher ID1-expressing astrocyte-like DIPG cells share a similar transcriptional program with ID1+/SPARCL1+ positive oligo/astrocyte-precursor (OAPC) cells from the developing human brain and demonstrate upregulation of gene sets involved in regulation of cell migration. Both genetic and pharmacologic [cannabidiol (CBD)] suppression of ID1 result in decreased DIPG cell invasion/migration in vitro and invasion/tumor growth in multiple in vivo models. Mechanistically, CBD reduces proliferation through production of reactive oxygen species. Further, DIPG patients treated off-trial with CBD (n=15) displayed reduced ID1 tumor expression and improved overall survival. In summary, ID1 is upregulated in DIPG through K27M-mediated epigenetic reactivation of a developmental OAPC-like transcriptional state, and ID1-driven invasiveness of DIPG is therapeutically targetable with CBD.

Characteristics of Patients ≥ 10 Years of Age with Diffuse Intrinsic Pontine Glioma: A Report from the International DIPG Registry

BACKGROUND

DIPG generally occurs in young school-age children, although can occur in adolescents and young adults. The purpose of this study was to describe clinical, radiological, pathologic, and molecular characteristics in patients ≥10 years of age with DIPG enrolled in the International DIPG Registry (IDIPGR).

METHODS

Patients ≥10 years of age at diagnosis enrolled in the IDIPGR with imaging confirmed DIPG diagnosis were included. The primary outcome was overall survival (OS) categorized as long-term survivors (LTS) (≥24 months) or short-term survivors (STS) (<24 months).

RESULTS

Among 1010 patients, 208 (21%) were ≥10 years of age at diagnosis; 152 were eligible with a median age of 12 years [range 10-26.8]. Median OS was 13 [2-82] months. The 1-, 3- and 5- years OS was 61.9%, 3.7%, and 1.5%, respectively. The 18/152 (11.8%) LTS were more likely to be older (P<0.01) and present with longer symptom duration (P<0.01). Biopsy and/or autopsy were performed in 50 (33%) patients; 77%, 61%, 33%, and 6% of patients tested had H3K27M (H3F3A or HIST1H3B), TP53, ATRX, and ACVR1 mutations/genome alterations, respectively. Two of 18 patients with IDH1 testing were IDH1-mutant and one was a LTS. The presence or absence of H3 alterations did not affect survival.

CONCLUSION

Patients ≥10 years old with DIPG have a median survival of 13 months. LTS present with longer symptom duration and are likely to be older at presentation compared to STS. ATRX mutation rates were higher in this population than the general DIPG population.

Adamantinomatous craniopharyngioma associated with a compromised blood–brain barrier: patient series

BACKGROUND

Adamantinomatous craniopharyngioma (ACP) is a highly morbid adult and pediatric brain tumor derived from epithelial remnants of the craniopharyngeal canal (Rathke’s pouch), which gives rise to the anterior pituitary gland. Standard therapy includes maximal safe resection with or without radiation therapy. Systemic antitumor therapy remains elusive. Immune-related paracrine signaling involving the interleukin-6 receptor (IL-6R) may contribute to ACP pathogenesis. Tocilizumab, a recombinant humanized monoclonal antibody against IL-6R, is approved by the US Food and Drug Administration but does not cross an intact blood–brain barrier.

OBSERVATIONS

In a phase 0 trial design, a single dose of tocilizumab was delivered intravenously before clinically indicated surgical intervention in 3 children with ACP. The presence of tocilizumab was assayed in plasma, tumor tissue, tumor cyst fluid, and cerebrospinal fluid (n = 1) using a novel enzyme-linked immunosorbent assay. Tocilizumab reached ACP tumor tissue and/or cyst fluid after one systemic dose in every patient.

LESSONS

This finding helps explain extant data that indicate tocilizumab may contribute to ACP therapy. It further indicates that ACP does not reside behind an intact blood–brain barrier, dramatically broadening the range of potential antitumor therapies against this tumor. This has substantial implications for the design of future clinical trials for novel therapies against ACP in both children and adults.

A Phase I and Surgical Study of Ribociclib and Everolimus in Children with Recurrent or Refractory Malignant Brain Tumors: A Pediatric Brain Tumor Consortium Study

PURPOSE

Genomic aberrations in cell cycle and PI3K pathways are commonly observed in pediatric brain tumors. This study determined the MTD/recommended phase II dose (RP2D) of ribociclib and everolimus and characterized single-agent ribociclib concentrations in plasma and tumor in children undergoing resection.

PATIENTS AND METHODS

Patients were enrolled in the phase I study according to a rolling 6 design and received ribociclib and everolimus daily for 21 and 28 days, respectively. Surgical patients received ribociclib at the pediatric RP2D (350 mg/m2) for 7-10 days preoperatively followed by enrollment on the phase I study. Pharmacokinetics were analyzed for both cohorts.

RESULTS

Sixteen patients were enrolled on the phase I study (median age, 10.3 years; range, 3.9-20.4) and 6 patients in the surgical cohort (median age, 11.4 years; range: 7.2-17.1). Thirteen patients were enrolled at dose level 1 without dose-limiting toxicities (DLT). Two of the 3 patients at dose level 2 experienced DLTs (grade 3 hypertension and grade 4 alanine aminotransferase). The most common grade 3/4 toxicities were lymphopenia, neutropenia, and leukopenia. The RP2D of ribociclib and everolimus was 120 and 1.2 mg/m2 for 21 and 28 days, respectively. Steady-state everolimus exposures with ribociclib were 2.5-fold higher than everolimus administered alone. Ribociclib plasma, tumor concentrations, and cerebrospinal fluid (CSF) samples were collected. The mean tumor-to-plasma ratio of ribociclib was 19.8 (range, 2.22-53.4).

CONCLUSIONS

Ribociclib and everolimus were well-tolerated and demonstrated pharmacokinetic properties similar to those in adults. Potential therapeutic ribociclib concentrations could be achieved in CSF and tumor tissue, although interpatient variability was observed.

MBCL-24. CAN YOUNG CHILDREN WITH RELAPSED MEDULLOBLASTOMA BE SALVAGED AFTER INITIAL IRRADIATION-SPARING APPROACHES?

INTRODUCTION

Irradiation-sparing approaches are used in young children with medulloblastoma (MB) given the vulnerability of the developing brain to neurocognitive impairment. Limited data are available following relapse for these patients. We aimed to describe the management and outcomes of young children with MB who relapsed after initial treatment without craniospinal irradiation (CSI).

METHODS

International retrospective study including patients with MB diagnosed between 1995–2017, ≤ 72 months old, initially treated without CSI, who subsequently relapsed.

RESULTS

Data are available for 52 patients (32 male). Median age at initial diagnosis was 27 months (range, 6–72) with 24 being metastatic. Initial therapy included conventional chemotherapy alone or high-dose chemotherapy (HDC) in 21 and 31 subjects, respectively. Three received upfront focal irradiation. Molecular subgrouping, available for 24 tumors, included 9 SHH and 15 non-WNT/non-SHH. Median time to relapse was 13 months (range, 3–63). Relapse was local, disseminated or combined in 20, 15, and 16, respectively. Salvage therapy with curative intent was given in 42/52 patients, including CSI in 28 subjects (median dose 36Gy, 18–41.4) or focal irradiation in 5 others. Three received HDC only. At a median follow-up time of 46 months (range, 4–255), 25 (48%) were alive, including 7/9 SHH and 7/15 non-WNT/non-SHH. The 2- and 5-year OS was 67% and 56% (SE, 7%), respectively. Two of 3 patients with SHH who did not receive salvage radiotherapy are survivors.

CONCLUSION

A substantial proportion of young children who relapse following irradiation-sparing strategies can be salvaged. Neurocognitive and ototoxicity outcomes are being evaluated.

QOL-36. USE OF CANNABINOIDS IN THE PEDIATRIC CENTRAL NERVOUS SYSTEM TUMOR POPULATION

BACKGROUND

Cannabinoids, including cannabidiol (CBD) and tetrahydrocannabinol (THC), are a class of compounds found in marijuana. Numerous studies in adults have examined cannabinoid use in management of cancer-related symptoms such as nausea, anorexia, and pain. Less is known about the use in the pediatric oncology population.

METHODS

A prospective observational study has been ongoing since 2016 at Children’s Hospital Colorado to evaluate cannabinoids’ impact using PedsQL™ modules on quality of life of pediatric patients with central nervous system (CNS) tumors who are 2–18 years old. Laboratory assessments of T-cell activity and pharmacokinetics of CBD, THC and associated metabolites are in process. Diaries with exploratory information on cannabinoid use patterns are being collected.

RESULTS

Thirty-three patients (14:19; male:female) have been enrolled with a median age of 6.4 years (range, 2.9–17.7 years). The most common tumor type in enrolled patients is embryonal tumors (13/33; 39%). Nine (27%) patients have low-grade glial/glioneuronal tumors, and eight (24%) had high-grade/diffuse midline gliomas. The remaining patients had ependymoma or craniopharyngioma. The median time on cannabinoids is 9 months. Most (n=20) patients have used oral products with CBD and THC. One patient continues on cannabinoid therapy in follow up. Preliminary immune function analyses identified impaired neutrophil superoxide anion production and chemotaxis in patients taking cannabinoids at early time points on therapy.

CONCLUSIONS

Families of children with various CNS tumors are pursuing cannabinoid therapy for both antitumor and supportive care purposes. Analysis of the impact of cannabinoids on patients’ quality of life is ongoing.

LGG-27. TARGETED THERAPY FOR PEDIATRIC LOW-GRADE GLIOMAS AND PLEXIFORM NEUROFIBROMAS WITH TRAMETINIB

BACKGROUND

Targeted therapy aimed at modulating the RAS/RAF/MEK/ERK pathway is of increasing interest for patients with plexiform neurofibromas and low-grade gliomas. Trametinib is an FDA-approved MEK inhibitor that has little published pediatric experience to date.

METHODS

A retrospective chart review of patients treated with trametinib for low-grade gliomas (LGG) and/or plexiform neurofibromas (PN) between 2015–2018 was conducted at Children’s Hospital Colorado. Data collected included patient demographics, lesion location, Neurofibromatosis type 1 (NF1) status, best response of PN/LGG to trametinib, duration of trametinib therapy, and reported toxicities at least possibly attributed to trametinib.

RESULTS

Thirty (57% male; 73% NF1) patients were identified. Sixteen (53%) patients had PN only, 12 (40%) had LGG only, and two (7%) patients had both PN and LGG. The most common LGG location was the optic pathway/hypothalamus (72%). The most common location of PN was the face (63%). Two-thirds (8/12) of patients with LGG had a BRAF alteration or NF1 mutation. The median age at start of trametinib therapy was 9.9 years (range, 2.0 – 18.8 years). The median duration of trametinib therapy was 0.8 years (range 0.1 – 2.9 years). The most commonly reported adverse event was rash. No patients developed retinal toxicity or cardiotoxicity. Only two (7%) patients discontinued for toxicity and one (3%) for progressive disease.

CONCLUSIONS

Trametinib can be administered without significant toxicity to children with PN or LGG. Clinical benefit is noted in this cohort; however, prospective clinical trials are necessary to characterize efficacy formally.

DIPG-42. TOWARD MULTIMODALITY THERAPY FOR DIPG/DMG: DEVELOPMENT AND INVESTIGATION OF CRANIOSPINAL IRRADIATION AND CONVECTION-ENHANCED DELIVERY PDX MODELS

BACKGROUND

Diffuse intrinsic pontine glioma (DIPG) and diffuse midline glioma (DMG) are metastatic diseases, as demonstrated by early convection-enhanced delivery (CED) clinical trials in which prolonged local tumor control can sometimes be achieved, but fatal disseminated disease then develops. We hypothesize that improvements in treatment of both focal disease and the entire neuraxis are necessary for long-term survival, and patient-derived xenograft (PDX) models can help advance these efforts.

METHODS

We used a BT245 murine orthotopic DIPG PDX model for this work. We developed a protocol and specialized platform to deliver craniospinal irradiation (CSI) with a pontine boost. We separately compared intratumoral drug concentration by CED and intraperitoneal delivery. In our CED model, mice receive gemcitabine 60 ug x1 in 15 ul at 0.5 ul/minute through a stepped catheter design with silica tubing extending 2mm beyond a 27G needle.

RESULTS

Mice receiving CSI (4 Gy x2d) plus boost (4 Gy x2d) showed minimal spinal and brain leptomeningeal metastatic disease by bioluminescence, MRI, and pathology compared to mice receiving radiation to the pons only (4 Gy x4d) or no radiation. CED achieved an intratumoral gemcitabine concentration 50-fold greater than intraperitoneal dosing when controlled for dose.

CONCLUSIONS

In a DIPG PDX model, CSI+boost minimizes tumor dissemination compared to focal radiation, and CED achieves clinically significant improvements in intratumoral chemotherapy concentration compared to systemic delivery. Adding these modalities to current treatment could improve both focal and metastatic tumor control, leading to meaningful improvements in survival.

DIPG-46. NON-DIPG PATIENTS ENROLLED IN THE INTERNATIONAL DIPG REGISTRY: HISTOPATHOLOGIC EVALUATION OF CENTRAL NEURO-IMAGING REVIEW

INTRODUCTION

The role of diagnostic biopsy in diffuse intrinsic pontine glioma (DIPG) remains in question. Distinguishing radiographically between DIPG and other pontine tumors with more favorable prognosis and different therapy is critically important.

METHODS

Cases submitted to the International DIPG registry with histopathologic data were analyzed. Central imaging review was performed by two neuro-radiologists; all cases with imaging features or histopathology suggestive of alternative diagnoses were re-reviewed. Imaging features suggestive of alternative diagnoses included non-pontine origin, <50% pontine involvement (without typical DIPG pattern on follow-up), focally exophytic morphology, sharply-defined margins, or marked diffusion restriction throughout.

RESULTS

Among 297 patients with pathology from biopsy and/or autopsy available, 27 (9%) had histologic diagnoses not consistent with DIPG, commonly embryonal tumors (n=9) and pilocytic astrocytomas (n=11). 163 patients had diagnostic MRI available for central neuroimaging review. Among 81 patients classified as characteristic of DIPG, 80 (99%) had histopathology consistent with DIPG (diffuse midline glioma, H3K27M-mutant, glioblastoma, anaplastic astrocytoma, diffuse astrocytoma). Among 63 patients classified as likely DIPG, but with unusual imaging features, 59 (94%) had histopathology consistent with DIPG. 19 patients had imaging features suggestive of another diagnosis, including 13 with non-pontine tumor origin; the remaining 6 all had histopathology not consistent with DIPG. Association between central imaging review and histopathology was significant (p<0.001).

CONCLUSIONS

The important role and accuracy of central neuroimaging review in diagnosing or excluding DIPG is demonstrated. In patients with pontine tumors for which DIPG is felt unlikely radiographically, biopsy may be considered to guide diagnosis and treatment.

RARE-10. ADAMANTINOMATOUS CRANIOPHARYNGIOMA RESIDES OUTSIDE THE BLOOD BRAIN BARRIER

BACKGROUND

Adamantinomatous craniopharyngioma (ACP) is a devastating skull-base tumor believed to derive from epithelial remnants of the primordial craniopharyngeal duct (Rathke’s pouch), which gives rise to the anterior pituitary gland. Genetically engineered mouse models of ACP demonstrate that perturbation of the fetal anterior pituitary can generate tumors analogous to ACP. Clinical and preclinical data indicate that IL-6 blockade may contribute to ACP tumor control, with the most common agent being the humanized monoclonal antibody, tocilizumab. This agent demonstrated poor blood-brain barrier (BBB) penetration in primates. We present findings from two children enrolled on a phase 0 clinical trial (NCT03970226) of a single dose of preoperative intravenous tocilizumab prior to resection of newly diagnosed ACP.

METHODS

Blood samples were obtained at multiple timepoints. Serum was isolated via ficoll separation. Tumor tissue and cyst fluid were obtained 4–6 hours following the single IV dose of tocilizumab. Tissue was snap-frozen. Tumor was homogenized in RIPA buffer. Free tocilizumab in serum, cyst fluid, and tumor tissue was measured using enzyme-linked immunosorbent assay (ELISA) against a standard curve.

RESULTS

Both patients in this trial demonstrated clinically relevant levels of tocilizumab (≥ 4µg/mL) in serum, cyst fluid, and tumor tissue, compared to undetectable levels in control samples.

CONCLUSION

ACP resides outside BBB protection. In addition to demonstrating the feasibility of systemic delivery of tocilizumab, these findings indicate that other large molecules, including those known to have poor BBB penetration, may be systemically delivered as part of an antitumor regimen in the treatment of ACP.

NURS-12. MAKING SURVIVORS HEALTHIER: A MULTIDISCIPLINARY APPROACH TO HYPOTHALAMIC OBESITY

BACKGROUND

Pediatric survivors of hypothalamic/suprasellar tumors have significant morbidities that greatly impact their quality of life. Management of hypothalamic obesity has traditionally fallen between multiple subspecialties without a timely and comprehensive approach.

METHODS

A multidisciplinary group of key players from neuro-oncology, endocrinology, nutrition, neurosurgery, and bariatric surgery were identified. Through this collaboration, a clinical algorithm for early identification of and intervention for hypothalamic obesity was developed. The goal of the quality improvement process is to increase the number of encounters with a registered dietitian (RD) with earlier and more consistent referrals to a specialized, multidisciplinary weight management program [Lifestyle Medicine; (LM)] for counseling and pharmacologic interventions. Indications for referral to LM were BMI &gt;95th percentile, crossing &gt;2 BMI percentiles on growth curve and/or hyperphagia symptoms. A retrospective review of pediatric patients who have suprasellar/ hypothalamic tumors was also conducted. Data collected included demographics, tumor type, BMI, RD visit, and LM clinic referral/visit.

RESULTS

Fifty patients were identified for analysis six months following clinical algorithm institution. Thirty-three (66%) patients had craniopharyngioma, 15 (30%) had low-grade gliomas, and two (4%) had germ cell tumors. Thirty-three (66%) patients were noted to be obese (defined as BMI &gt;95th percentile) at review. The median BMI of the entire cohort was 93rd (range, 1st-137th) percentile. Thirty-four (68%) patients had been seen by an RD. Twenty-seven (82%) of the obese patients had been referred to LM.

CONCLUSIONS

The development and implementation of the process for hypothalamic obesity prevention and intervention will be discussed.

RARE-08. CYST FLUID CYTOKINES MAY PROMOTE EPITHELIAL-TO-MESENCHYMAL TRANSITION IN PEDIATRIC ADAMANTINOMATOUS CRANIOPHARYNGIOMA

BACKGROUND

Despite poor clinical outcomes, no targeted therapies have been established for the treatment of Adamantinomatous Craniopharyngioma (ACP). The only known genetic aberration is a mutation in CTNNB1 that results in the nuclear accumulation of beta-catenin. Nuclear beta-catenin is an established inducer of Epithelial-to-Mesenchymal Transition (EMT). ACP cyst fluid is enriched with pro-inflammatory and SASP cytokines, many of which are also directly implicated in EMT. We sought to investigate the role of EMT in ACP pathology.

METHODS

Normal human epithelial cells were cultured and treated with ACP cyst fluid (10%) for 1, 2, 4 and 8 days. Cell morphology was monitored by live cell brightfield microscopy. The expression of EMT associated genes, ZEB1, ZEB2, SNAI-1, SLUG, TWIST, E-Cadherin, Beta-Catenin and Vimentin was determined by RT-qPCR.

RESULTS

ACP cyst fluid treated epithelial cells were markedly transformed into long, spindle-shaped cells. ACP cyst fluid treatment resulted in the progressive up-regulation of ZEB2 over 8 days (RQ=12.0; P&lt;0.01), the progressive up-regulation of SNAI-1 over 4 days (RQ=5.1; P&lt;0.05) and up-regulation of Vimentin (RQ=2.2; p&lt;0.01), identified only on Day 8.

CONCLUSION

ACP cyst fluid can induce EMT-like changes in normal human epithelial cells. In conjunction with the frequency of beta-catenin mutation in ACP, it is possible that EMT plays a crucial role in the pathology of ACP. Understanding ACP pathology in the context of the EMT paradigm may aid the development of new targeted therapeutics.

HGG-57. WHOLE-GENOME SEQUENCING, METHYLATION ANALYSIS, AND SINGLE-CELL RNA-SEQ DEFINE UNIQUE CHARACTERISTICS OF PEDIATRIC TREATMENT-INDUCED HIGH-GRADE GLIOMA AND SUGGEST ONCOGENIC MECHANISMS

BACKGROUND

Pediatric treatment-induced high-grade glioma (TIHGG) is among the most severe late effects observed in childhood cancer survivors and is uniformly fatal. We previously showed that TIHGG are divergent from de novo pediatric high-grade glioma (pHGG) and cluster into two gene expression subgroups, one stemlike and the other inflammatory. Here we systematically compared TIHGG molecular profiles to pHGG and evaluated expression and single cell sequencing profiles in order to identify oncogenic mechanisms and the cellular basis for the observed TIHGG gene expression subgroups. MATERIALS/

METHODS

450/850K methylation and mutational signature analysis was conducted in 36 TIHGG samples. Resultant data were analyzed for the presence of chromothripsis, distinct molecular alterations, and mutational signatures in a subset of 10 samples with whole genome sequencing data. Five TIHGGs underwent single-cell RNA-Seq analysis (scRNAseq).

RESULTS

26/36 TIHGG clustered with the pedRTK1 methylation class. TIHGG were characterized by an increased frequency of chromothripsis relative to pHGG (67% vs. 31%, p=0.036). FISH and WGS revealed frequent PDGFRA amplification secondary to enrichment in ecDNA. TIHGG were enriched for COSMIC mutational signatures 5 and 19 (p=0.0003) relative to pHGG. scRNAseq data showed that TIHGG tumors are composed of stem-like, neuronal, and inflammatory cell populations which may contribute to the previously described dominant expression profiles.

CONCLUSIONS

TIHGG represents a distinct molecular subtype of pHGG. Chromothripsis, leading to enriched expression of genes in extrachromosomal DNA, likely contribute to TIHGG oncogenesis. The dominant cell type (stem-like vs. inflammatory) may define the expression subgroup derived from bulk RNA-seq in heterogeneous tumors.

EPCT-18. PHASE 0/I STUDY OF GM-CSF AND INTRATHECAL TRASTUZUMAB IN CHILDREN WITH RECURRENT POSTERIOR FOSSA EPENDYMOMA

BACKGROUND

Posterior fossa ependymoma (PF EPN) is a pediatric central nervous system malignancy that has a poor outcome to standard therapeutic approaches. The majority of PF EPN tumors have increased HER2 expression. Trastuzumab is a monoclonal antibody that targets HER2, and sargramostim (GM-CSF) stimulates hematopoietic progenitor cell proliferation. The combination of trastuzumab and GM-CSF has been shown to trigger antibody-dependent cell cytotoxicity in vitro in PF EPN cell lines.

METHODS

Children aged 1–21 years with relapsed PF EPN and no ventriculoperitoneal shunt or CSF obstruction are eligible for the Phase 0/I institutional trial at Children’s Hospital Colorado. Stratum 1 involves IT trastuzumab and subcutaneous (subQ) GM-CSF prior to standard-of-care surgical resection. Stratum 2 involves a 3 + 3 phase I design with serial IT trastuzumab doses, each preceded by three days of GM-CSF, to establish the MTD for IT trastuzumab.

RESULTS

Trastuzumab was detected in a sufficient number of tumors after presurgical IT delivery in Stratum 1 to open Stratum 2. Four patients (75% female) have been enrolled in Stratum 2 at trastuzumab Dose Level 1. Median age at enrollment is 9.8 years (range, 3.5–20.2 years). Preliminary CSF pharmacokinetic analysis demonstrated detectable trastuzumab up to 14 days after IT doses. No dose-limiting toxicities have occurred. Two patients progressed on therapy (median, 4 cycles). One patient is progression-free at 18 months off therapy. One patient remains on study therapy.

CONCLUSIONS

IT trastuzumab penetrates PF EPN tumor tissue. Stratum 2 remains open to accrual at Dose Level 2.

OTHR-16. CONCURRENT USE OF APREPITANT AND IFOSFAMIDE IN PEDIATRIC CANCER PATIENTS

BACKGROUND

Aprepitant, a selective neurokinin-1 receptor antagonist, is commonly used for prevention of chemotherapy-induced nausea and vomiting. Its use with ifosfamide is controversial due to the putative risk of potentiating neurotoxicity via inhibition of cytochrome P450 3A4 (CYP3A4). The current literature examining this interaction is inconclusive, and little data exists in pediatrics. We seek to describe a single-institution experience with concurrent aprepitant and ifosfamide administration.

METHODS

A retrospective review of patients treated with ifosfamide and aprepitant from 2009–2018 was conducted. Data collected included demographics, tumor type, number of days of concurrent therapy, dosing, and documented of neurotoxicity.

RESULTS

Twenty patients aged 7–21 years (median 17 years) were identified. Diagnoses included thirteen sarcomas and seven CNS tumors (6 germ cell tumors; 1 intracranial sarcoma). Five patients received high dose ifosfamide (>2,000mg/m²/day). The number of concurrent ifosfamide and aprepitant doses ranged from 2–18 (median, 8.5). Only one patient (5%) developed ifosfamide-induced neurotoxicity: a 7-year-old female with a nongerminomatous germ cell tumor who presented with seizures and somnolence. She received methylene blue and returned to her neurologic baseline. She completed her ifosfamide course without incident. She was the only patient to require weight-based aprepitant dosing and to receive the liquid formulation.

CONCLUSIONS

Aprepitant should be used with caution when administered concurrently with ifosfamide due to the risk of neurotoxicity. However, the incidence of neurotoxicity in this retrospective pediatric cohort was low. This interaction may be more significant in younger patients due to age-related differences in hepatic metabolism, but further study is required.

DIPG-55. PATTERNS OF CEREBROSPINAL FLUID DIVERSION AND SURVIVAL IN CHILDREN WITH DIFFUSE INTRINSIC PONTINE GLIOMA: A REPORT FROM THE INTERNATIONAL DIPG REGISTRY

There is no standard of care for cerebrospinal (CSF) diversion in children with diffuse intrinsic pontine glioma (DIPG), nor understanding of survival impact. We evaluated CSF diversion characteristics in children with DIPG to determine incidence, indications and potential impact on survival. Data was extracted from subjects registered in the International DIPG registry (IDIPGR). IDIPGR team personnel obtained clinical and radiographic data from the registry database and when appropriate, abstracted additional data from individual medical records. Univariable analyses were performed using the Fisher’s exact test or Wilcoxon rank sum test. Survival was estimated using the Kaplan-Meier method. Evaluable patients (n=457) met criteria for DIPG diagnosis by central radiology review. Ninety-two patients (20%) had permanent CSF diversion. Indications for permanent diversion were hydrocephalus (41%), hydrocephalus and clinical symptoms (35%), and clinical symptoms alone (3%). Those with permanent diversion were significantly younger at diagnosis than those without diversion (median 5.3 years vs 6.9 years, p=0.0002), otherwise no significant differences in gender, race, or treatment were found. The progression-free and overall survival of those with permanent CSF diversion compared to those without permanent diversion was 4.5 and 10.9 months vs 6.9 and 11.2 months, respectively (p=0.001, p= 0.4). There was no significant difference in overall survival in patients with or without permanent CSF diversion among a large cohort of DIPG patients. Patients without permanent diversion had significantly prolonged progression free survival compared to those with permanent diversion. The qualitative risks and benefits of permanent CSF diversion need to be further evaluated.

LGG-52. BINIMETINIB IN CHILDREN WITH PROGRESSIVE OR RECURRENT LOW-GRADE GLIOMA NOT ASSOCIATED WITH NEUROFIBROMATOSIS TYPE 1: INITIAL RESULTS FROM A MULTI-INSTITUTIONAL PHASE II STUDY

BACKGROUND

RAS/RAF/MEK/ERK pathway activation is the primary driver for most pediatric low-grade gliomas (LGG). Binimetinib is an orally bioavailable MEK1/2 inhibitor found to have significant central nervous system penetration in a preclinical model.

OBJECTIVE

The primary objective of this multi-institutional open-label phase II study was to assess preliminary efficacy of binimetinib in progressive pediatric LGG. The study included strata for both neurofibromatosis type I (NF1) and non-NF1 associated tumors, as well as a target validation (surgical) stratum. NF1 and surgical strata remain open to enrollment and will be reported separately.

METHODS

Children aged 1–18 years with previously treated recurrent or progressive LGG were eligible. The dose of binimetinib was 32 mg/m²/dose twice daily. Partial and minor responses were defined, respectively, as 50% and 25% decrease in maximal two-dimensional measurements.

RESULTS

Fifty-seven eligible patients without NF1, median age 8 years, were enrolled and began treatment; 26 were female; 28 had documented KIAA1549-BRAF fusion. Eleven patients discontinued drug in the first year due to toxicity, and an additional 27 required dose reduction. The most common drug-attributable grade 3 toxicities included creatine kinase elevation (n=9 patients), rash (n=8), and truncal weakness (n=8). Truncal weakness improved or resolved with dose reduction or cessation. Grade 4 toxicities included creatine kinase elevation (n=2) and transient colitis (n=1). Of 44 patients with preliminary response data available, 22 (50%) showed a minor (n=7) or partial (n=15) response.

CONCLUSION

Binimetinib is active, with manageable toxicities, in children without NF1 with progressive LGG.

EPCT-17. A PHASE I AND SURGICAL STUDY OF RIBOCICLIB AND EVEROLIMUS IN CHILDREN WITH RECURRENT OR REFRACTORY MALIGNANT BRAIN TUMORS: PEDIATRIC BRAIN TUMOR CONSORTIUM INTERIM REPORT

Genomic aberrations in the cell cycle and PI3K pathway are commonly observed in recurrent childhood brain tumors. Dual inhibition of CDK4/6 (ribociclib) and mTOR (everolimus) has strong biologic rationale, non-overlapping single-agent toxicities, and adult clinical experience. The maximum tolerated dosage (MTD) and/or recommended phase two dose (RP2D) of ribociclib and everolimus was determined in the Phase I study and ribociclib concentrations were characterized in plasma and tumor in children undergoing neurosurgical procedures. Following resection, eligible patients were enrolled in the Phase I study according to a rolling 6 design and received ribociclib and everolimus once daily for 21 days and 28 days, respectively. Patients undergoing surgery received ribociclib at the pediatric RP2D (350 mg/m²/day) for 7–10 days pre-operatively. Pharmacokinetic samples were collected on both cohorts and analyzed in nine patients on phase I study. Sixteen eligible patients enrolled on phase I study (median age 10.3 years; range: 3.9–20.4) and 5 patients were enrolled on the surgical cohort (median age 11.4 years; range: 7.2–17.1). Six patients enrolled at dose level 1 without dose limiting toxicities (DLT). Two of the three patients at dose level 2 experienced DLT (grade 3 hypertension and grade 4 ALT). The most common grade 3/4 toxicities were lymphopenia, neutropenia, and leucopenia. Everolimus concentrations following administration of everolimus alone were lower than those following drug combination, suggesting an impact of ribociclib on everolimus pharmacokinetics. The MTD/RP2D of ribociclib and everolimus in recurrent CNS tumors is 120 mg/m² and 1.2 mg/ m² daily for 21 days and 28 days, respectively.

DIPG-74. RE-IRRADIATION OF DIPG: DATA FROM THE INTERNATIONAL DIPG REGISTRY

PURPOSE

To review data from DIPG Registry patients recorded to have received a second course of radiation therapy (rRT).

METHODS

The International DIPG Registry was searched for patients with DIPG who were treated with a known dose of rRT. Doses of rRT, timing from initial diagnosis and primary radiation therapy (pRT), radiographic response to rRT and survival from diagnosis (OS) were evaluated.

RESULTS

Sixty (11.2%) of 535 Registry patients underwent rRT; dose was provided for 44 patients. Median (range) data from those 44 revealed that rRT was given at 12 (2–65) months from initial diagnosis of DIPG and at 9.6 (1–61) months from completion of pRT at a dose of 26.7 (1.8–74) Gy. After completion of rRT, MRI showed response, progression, stable disease or was not available in 19, 8, 3 and 14 patients, respectively. Median PFS and OS were 11 and 18.1 months, respectively. 475 Registry patients did not undergo rRT; their ages, duration of symptoms, and primary treatment with or without chemotherapy were not significantly different from the rRT cohort. Median PFS and OS for the non-rRT patients were 6.9 and 10 months, respectively. rRT patients were more likely to have had radiographic evidence of tumor necrosis at diagnosis than non-rRT patients.

CONCLUSIONS

Administration of rRT to patients with DIPG has been inconsistent with respect to timing and dose. Toxicity, response and quality of life data are incomplete, but survival appears to be lengthened with rRT. Prospective clinical trials will elucidate benefits and risks of rRT.

NCOG-47. CAN YOUNG CHILDREN WITH RELAPSED MEDULLOBLASTOMA BE SALVAGED AFTER INITIAL IRRADIATION-SPARING APPROACHES?

INTRODUCTION

Irradiation-sparing approaches are used in young children with medulloblastoma (MB) given the vulnerability of the developing brain to neurocognitive impairment. Limited data are available following relapse for these patients. We aimed to describe the management and outcomes of young children with MB who relapsed after initial treatment without craniospinal irradiation (CSI).

METHODS

International retrospective study including patients with MB diagnosed between 1995-2017, ≤ 72 months old, initially treated without CSI, who subsequently relapsed.

RESULTS

Data are available for 66 patients. The median age at initial diagnosis was 27 months (range, 6-72). At diagnosis, 27 patients had metastatic disease. Initial therapy included conventional chemotherapy or with high-dose chemotherapy (HDC) in 30 and 36 patients, respectively. Eight (12.1%) received upfront focal irradiation. Molecular subgrouping was available for 27 (41%) patients. Ten were SHH, five group 3, six group 4 and six others were non-WNT/non-SHH. The median time from initial diagnosis to relapse was 13 months (range, 3-63). Relapse was local, disseminated, or combined in 39%, 32%, and 29%, respectively. The median time to death from relapse was 18 months. Curative intent therapy was given in 53 patients with irradiation (81%), conventional chemotherapy without HDC (40%), and HDC (25%). For patients who received irradiation, 85% received CSI (median dose 33 Gy, 18-41.4) and 15% focal irradiation. Ten patients received chemotherapy without salvage irradiation. The median follow-up time was 44 months (range, 4-255), 33 (62%) patients who underwent curative-intent therapy were alive, including 8/10 SHH, 2/3 group 3, 2/6 group 4, and 4/5 non-WNT/non-SHH. Three of four patients with SHH and treated without salvage radiotherapy are survivors. The 5-year OS for curative intent was 70%.

CONCLUSION

A substantial proportion of young children who relapse following irradiation-sparing strategies can be salvaged. A proportion of children with SHH MB can be salvaged without salvage radiotherapy.

NIMG-31. NON-DIPG PATIENTS ENROLLED IN THE INTERNATIONAL DIPG REGISTRY: HISTOPATHOLOGIC EVALUATION OF CENTRAL NEURO-IMAGING REVIEW

INTRODUCTION

The role of diagnostic biopsy in diffuse intrinsic pontine glioma (DIPG) remains in question. Distinguishing radiographically between DIPG and other pontine tumors with more favorable prognosis and different therapy is critically important.

METHODS

Cases submitted to the International DIPG registry with histopathologic data were analyzed. Central imaging review was performed on diagnostic brain MRI (if available) by two neuro-radiologists; all cases with imaging features or histopathology suggestive of alternative diagnoses were re-reviewed. Imaging features suggestive of alternative diagnoses included non-pontine origin, &lt; 50% pontine involvement (without typical DIPG pattern on follow-up), focally exophytic morphology, sharply-defined margins, or marked diffusion restriction throughout.

RESULTS

Among 294 patients with pathology from biopsy and/or autopsy available, 27 (9%) had histologic diagnoses not consistent with DIPG, most commonly pilocytic astrocytomas (n=11) and embryonal tumors (n=9). Of these 294 patients with biopsy and/or autopsy pathologic data, 163 also had diagnostic MRI available for central neuroimaging review and radiographic comparison. Among 81 patients classified as characteristic of DIPG, 80 (99%) had histopathology consistent with DIPG (diffuse midline glioma, H3K27M-mutant, glioblastoma, anaplastic astrocytoma, diffuse astrocytoma). Among 63 patients classified as likely DIPG, but with unusual imaging features, 59 (94%) had histopathology consistent with DIPG. Nineteen patients had imaging features suggestive of another diagnosis, including 13 with non-pontine tumor origin; the remaining 6 patients all had histopathology not consistent with DIPG (embryonal tumors [n=3, including 1 with medulloblastoma], pilocytic astrocytoma [n=1], and ganglioglioma [n=1]). Association between central imaging review and histopathology was significant (p &lt; 0.001 by the Freeman-Halton Fischer Exact Probability Test).

CONCLUSIONS

The important role and accuracy of central neuroimaging review in diagnosing or excluding DIPG is demonstrated. In patients with pontine tumors for which DIPG is felt unlikely radiographically, biopsy may be considered to guide diagnosis, prognosis, and treatment.

Retrospective analysis of combination carboplatin and vinblastine for pediatric low-grade glioma

INTRODUCTION

Low-grade glioma (LGG) represent the most common pediatric central nervous system tumor. When total surgical resection is not feasible, chemotherapy is first-line therapy in children. Multiple pediatric LGG chemotherapy regimens have been investigated with variable 2-year event free survival (EFS) rates of 39-69%. To date, treatment of pediatric LGG with a carboplatin and vinblastine (C/VBL) chemotherapy regimen has only been evaluated in a phase 1 dose-finding study.

METHODS

A retrospective review of pediatric patients with LGG who were treated with C/VBL at Children's Hospital of Colorado or Akron Children's Hospital from 2011 to 2017 was conducted. Data collected included patient demographics, tumor location, disease response, neurofibromatosis 1 (NF1) status, therapy duration and toxicities. Response to therapy was determined by objective findings on imaging and treating physicians' evaluation.

RESULTS

Forty-six patients were identified for analysis, all of whom were chemotherapy-naive. Only five patients treated in this cohort had NF1. BRAF fusion was identified in 65% (22/34) of tested tumors. Best therapy response was partial response in nine patients and stable disease in twenty-five patients. Twelve patients had progressive disease. One-year, 3-year, and 5-year EFS probabilities for all patients were 69.6%, 39.4%, and 34.5%, respectively. Nine patients had admissions for febrile neutropenia and seven patients experienced one delay in chemotherapy due to neutropenia. Only two patients had to discontinue this chemotherapy regimen because of treatment-related toxicities [carboplatin allergy (n = 1) and vinblastine neuropathy (n = 1)].

CONCLUSION

C/VBL achieves similar EFS rates to other single-agent and combination cytotoxic chemotherapy regimens for pediatric LGG with manageable toxicities.

Preclinical and clinical investigation of intratumoral chemotherapy pharmacokinetics in DIPG using gemcitabine

Background

Hundreds of systemic chemotherapy trials in diffuse intrinsic pontine glioma (DIPG) have not improved survival, potentially due to lack of intratumoral penetration, which has not previously been assessed in humans.

Methods

We used gemcitabine as a model agent to assess DIPG intratumoral pharmacokinetics (PK) using mass spectrometry.

Results

In a phase 0 clinical trial of i.v. gemcitabine prior to biopsy in children newly diagnosed with DIPG by MRI, mean concentration in 4 biopsy cores in patient 1 (H3K27M diffuse midline glioma) was 7.65 µM. These compare favorably to levels for patient 2 (mean 3.85 µM, found to have an H3K27-wildtype low-grade glioma on histology), and from a similar study in adult glioblastoma (adjusted mean 3.48 µM). In orthotopic patient-derived xenograft (PDX) models of DIPG and H3K27M-wildtype pediatric glioblastoma, gemcitabine levels and clearance were similar in tumor, pons, and cortex and did not depend on H3K27 mutation status or tumor location. Normalized gemcitabine levels were similar in patient 1 and the DIPG PDX.

Conclusions

These findings, while limited to one agent, provide preliminary evidence for the hypotheses that lack of intratumoral penetration is not why systemic chemotherapy has failed in DIPG, and orthotopic PDX models can adequately model intratumoral PK in human DIPG.

Targeted fusion analysis can aid in the classification and treatment of pediatric glioma, ependymoma, and glioneuronal tumors

BACKGROUND

The use of next-generation sequencing for fusion identification is being increasingly applied and aids our understanding of tumor biology. Some fusions are responsive to approved targeted agents, while others have future potential for therapeutic targeting. Although some pediatric central nervous system tumors may be cured with surgery alone, many require adjuvant therapy associated with acute and long-term toxicities. Identification of targetable fusions can shift the treatment paradigm toward earlier integration of molecularly targeted agents.

METHODS

Patients diagnosed with glial, glioneuronal, and ependymal tumors between 2002 and 2019 were retrospectively reviewed for fusion testing. Testing was done primarily using the ArcherDx FusionPlex Solid Tumor panel, which assesses fusions in 53 genes. In contrast to many previously published series chronicling fusions in pediatric patients, we compared histological features and the tumor classification subtype with the specific fusion identified.

RESULTS

We report 24 cases of glial, glioneuronal, or ependymal tumors from pediatric patients with identified fusions. With the exception of BRAF:KIAA1549 and pilocytic/pilomyxoid astrocytoma morphology, and possibly QKI-MYB and angiocentric glioma, there was not a strong correlation between histological features/tumor subtype and the specific fusion. We report the unusual fusions of PPP1CB-ALK, CIC-LEUTX, FGFR2-KIAA159, and MN1-CXXC5 and detail their morphological features.

CONCLUSIONS

Fusion testing proved to be informative in a high percentage of cases. A large majority of fusion events in pediatric glial, glioneuronal, and ependymal tumors can be identified by relatively small gene panels.

Establishment of patient-derived orthotopic xenograft model of 1q+ posterior fossa group A ependymoma

BACKGROUND

Treatment for pediatric posterior fossa group A (PFA) ependymoma with gain of chromosome 1q (1q+) has not improved over the past decade owing partially to lack of clinically relevant models. We described the first 2 1q+ PFA cell lines, which have significantly enhanced our understanding of PFA tumor biology and provided a tool to identify specific 1q+ PFA therapies. However, cell lines do not accurately replicate the tumor microenvironment. Our present goal is to establish patient-derived xenograft (PDX) mouse models.

METHODS

Disaggregated tumors from 2 1q+ PFA patients were injected into the flanks of NSG mice. Flank tumors were then transplanted into the fourth ventricle or lateral ventricle of NSG mice. Characterization of intracranial tumors was performed using imaging, histology, and bioinformatics.

RESULTS

MAF-811_XC and MAF-928_XC established intracranially within the fourth ventricle and retained histological, methylomic, and transcriptomic features of primary patient tumors. We tested the feasibility of treating PDX mice with fractionated radiation or chemotherapy. Mice tolerated radiation despite significant tumor burden, and follow-up imaging confirmed radiation can reduce tumor size. Treatment with fluorouracil reduced tumor size but did not appear to prolong survival.

CONCLUSIONS

MAF-811_XC and MAF-928_XC are novel, authentic, and reliable models for studying 1q+ PFA in vivo. Given the successful response to radiation, these models will be advantageous for testing clinically relevant combination therapies to develop future clinical trials for this high-risk subgroup of pediatric ependymoma.

Abstract C002: Phase 1 study of abemaciclib in children with recurrent and refractory solid tumors including malignant brain tumors

Background: Cyclin-dependent kinases 4 and 6 (CDK4/6) control the transition between G1 and S phases of the cell cycle and are dysregulated in a number of pediatric brain and solid tumors. Abemaciclib, a selective and potent small molecule CDK4/6 inhibitor that crosses the blood brain barrier, limits cell proliferation by suppressing phosphorylation of RB, leading to G1 arrest. Methods: We conducted a phase 1 trial of abemaciclib to determine the maximum tolerated dose (MTD), describe toxicities, and pharmacokinetic (PK) parameters of abemaciclib in pediatric patients with recurrent or refractory solid and CNS tumors. A stratum for newly diagnosed patients with diffuse midline glioma continues to enroll. A CDK mutation was not required, and patients with known RB1 mutations were excluded. Abemaciclib was administered orally twice daily on days 1-28 of a 28-day cycle. Four dose levels were planned (100, 130, 170, and 220 mg/m2/dose) and evaluated using a rolling-six design. Patients were enrolled to a dose expansion cohort at the MTD to ensure adequate PK sampling and safety. PK and pharmacodynamic (PD) analyses are ongoing. Results: The median age of 34 eligible patients was 13.8 years (range: 2.9 - 23.2). Seven (21%) patients had a solid tumor [osteosarcoma (N=2), neuroblastoma (N=1), rhabdomyosarcoma (N=1), desmoplastic small round cell tumor (N=1), clear cell sarcoma (N=1), and MRT of kidney (N=1)] and 27 (79%) patients had a malignant brain tumor [high-grade glioma (N=12), DIPG (N=5), ATRT (N=3), medulloblastoma (N=3), ependymoma (N=2), PNET (N=1), and CNS neuroblastoma (N=1)]. Twenty-three patients were evaluable for DLT. There were 2 cycle 1 DLTs, grade 4 thrombocytopenia and grade 3 vomiting and diarrhea, both occurring at dose level 3. The most common treatment-related cycle 1 adverse events were leukopenia (69%), neutropenia (53%), thrombocytopenia (44%), hypoalbuminemia (41%), anemia (38%), hypophosphatemia (34%) and diarrhea (34%). Conclusions: The pediatric MTD of abemaciclib was 130 mg/m2/dose administered orally twice daily on a 28-day cycle. Abemaciclib was well-tolerated with mainly hematologic toxicity. PK and PD will be used to further inform if 130 mg/m2/dose is the pediatric recommended phase 2 dose.

Citation Format: Thomas Cash, Dolly Aguilera, Margaret E Macy, Lindsey Hoffman, Kathleen Dorris, Courtney McCracken, Bradley Hanberry, Robert Castellino, Tobey MacDonald, Cynthia Wetmore. Phase 1 study of abemaciclib in children with recurrent and refractory solid tumors including malignant brain tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C002. doi:10.1158/1535-7163.TARG-19-C002

PDCT-13. ENTRECTINIB IN CHILDREN AND ADOLESCENTS WITH RECURRENT OR REFRACTORY SOLID TUMORS INCLUDING PRIMARY CNS TUMORS

The phase 1/2 STARTRK-NG trial is evaluating entrectinib, a CNS-penetrant oral inhibitor of TRK, ROS1 and ALK tyrosine kinases, in children with solid tumors, including primary CNS tumors. Eligible patients are ≤22y with recurrent/refractory solid tumors. The recommended dose was determined in all-comers, and then expansion cohorts of CNS and solid tumors with NTRK1/2/3, ROS1 or ALK gene fusions, and neuroblastomas (NBL) regardless of mutation spectrum, were enrolled. Investigator-assessed response was classified as complete (CR) or partial response (PR), stable (SD) or progressive disease using RANO (CNS), RECIST (solid tumors), or Curie score (NBL). By the clinical data cut-off, 01 April 2019, 32 patients were enrolled. As of 31 Oct 2018 (enrollment data cut-off), 29 patients were enrolled and included in the evaluable population. Median age was 7y (range 4.9m to 20y). Entrectinib was well tolerated; phase 1 dose-limiting toxicities were: elevated creatinine, dysgeusia, fatigue, and pulmonary edema. The recommended dose was 550mg/m2 daily; all responses occurred at doses ≥400mg/m2. In 6 patients with high-grade CNS tumors, all gene-fusion-positive, ORR was 100% (Investigator-assessed responses): 2 CR (ETV6-NTRK3, EML1-NTRK2); 4 PR (TPR-NTRK1, KANK1-NTRK2, EEF1G-ROS1, GOPC-ROS1). In extracranial solid tumors 6/8 had a fusion; of these, 2 achieved a confirmed CR (DCTN1-ALK, ETV6-NTRK3), and 4 achieved PR (ETV6-NTRK3, EML4-NTRK3, TFG1-ROS1, KIF5B-ALK). Central imaging review is being performed and will be provided. Duration of therapy ranged from 0.2 to 22.2 months for all 32 patients. In responding patients, time to response ranged from 1 to 8.3 months. In children with refractory CNS tumors harboring NTRK1/2/3 or ROS1 fusions, entrectinib produced striking, rapid, and durable responses. No responses were seen in tumors lacking target gene fusions. These results support the continued evaluation of entrectinib in solid tumors with target gene fusions, especially high-grade CNS neoplasms.