A Case of Primary Intracranial Sarcoma, DICER1-Mutant, in a Child with a Germline DICER1 Mutation

DICER1 syndrome is a tumor predisposition syndrome caused by abnormal micro-RNA processing which leads to a variety of benign and malignant neoplasms in many organ systems, including the central nervous system. This paper reports the case of a primary intracranial sarcoma, DICER1-mutant, in a patient with a germline DICER1 variant thought most likely to be de novo. The patient is a ten-year-old boy who presented acutely with altered level of consciousness, emesis, and left-sided weakness. Imaging revealed a large right frontal hemorrhagic lesion, which was urgently debulked. Histology demonstrated a high-grade sarcomatous lesion. Molecular studies revealed compound heterozygous DICER1 variants (a frame shift insertion and a missense mutation), and a KRAS missense mutation. The final pathologic diagnosis was rendered to be "primary intracranial sarcoma, DICER1-mutant". Germline genetic testing revealed that the patient possessed a germline DICER1 variant (parental testing was negative). A dramatic reduction in tumor size was precipitated via chemotherapy (ifosfamide, carboplatin, and etoposide) and radiotherapy (focal proton beam therapy). There was no evidence of residual disease at the primary site at the end of the therapy.

3D genome mapping identifies subgroup-specific chromosome conformations and tumor-dependency genes in ependymoma

Ependymoma is a tumor of the brain or spinal cord. The two most common and aggressive molecular groups of ependymoma are the supratentorial ZFTA-fusion associated and the posterior fossa ependymoma group A. In both groups, tumors occur mainly in young children and frequently recur after treatment. Although molecular mechanisms underlying these diseases have recently been uncovered, they remain difficult to target and innovative therapeutic approaches are urgently needed. Here, we use genome-wide chromosome conformation capture (Hi-C), complemented with CTCF and H3K27ac ChIP-seq, as well as gene expression and DNA methylation analysis in primary and relapsed ependymoma tumors, to identify chromosomal conformations and regulatory mechanisms associated with aberrant gene expression. In particular, we observe the formation of new topologically associating domains ('neo-TADs') caused by structural variants, group-specific 3D chromatin loops, and the replacement of CTCF insulators by DNA hyper-methylation. Through inhibition experiments, we validate that genes implicated by these 3D genome conformations are essential for the survival of patient-derived ependymoma models in a group-specific manner. Thus, this study extends our ability to reveal tumor-dependency genes by 3D genome conformations even in tumors that lack targetable genetic alterations.

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.

Multi-institutional analysis of central nervous system germ cell tumors in patients with Down syndrome

PURPOSE

Primary germ cell tumors (GCTs) are the most common central nervous system (CNS) neoplasm in patients with Down syndrome (DS). However, a standard of care has not been established due to paucity of data.

METHODS

A retrospective multi-institutional analysis was conducted, in addition to a comprehensive review of the literature.

RESULTS

Ten patients from six institutions (five USA, one Brazil) were identified, in addition to 31 patients in the literature from 1975 to 2021. Of the 41 total patients (mean age 9.9 years; 61% male), 16 (39%) had non-germinomatous germ cell tumors (NGGCTs), 16 (39%) had pure germinomas, and eight (19.5%) had teratomas. Basal ganglia was the most common tumor location (n = 13; 31.7%), followed by posterior fossa (n = 7; 17%). Nine patients (22%) experienced disease relapse or progression, of which four died from tumor progression (one germinoma, three teratomas). Sixteen patients (39%) experienced treatment-related complications, of which eight (50%) died (five germinomas, three NGGCTs). Of the germinoma patients, two died from chemotherapy-related sepsis, one from postsurgery cardiopulmonary failure, one from pneumonia, and one from moyamoya following radiation therapy (RT). Of the NGGCT patients, one died from chemotherapy-related sepsis, one from postsurgical infection, and one from pneumonia following surgery/chemotherapy/RT. Three-year overall survival was 66% for all histological types: 62% germinomas, 79% for NGGCTs, and 53% for teratomas.

CONCLUSION

Patients with DS treated for CNS GCTs are at an increased risk of treatment-related adverse events. A different therapeutic approach may need to be considered to mitigate treatment-related complications and long-term neurocognitive sequelae.

GCT-15. Multi-institutional analysis and literature review of central nervous system germ cell tumors in patients with Down syndrome

BACKGROUND: A standard-of-care has not been established for the management of patients with Down syndrome (DS) who develop primary central nervous system (CNS) germ cell tumors (GCTs) – the most common CNS neoplasm in DS – despite being more susceptible to treatment-related adverse events. METHODS: Data from large academic institutions were collected and a comprehensive review of the medical literature was conducted. RESULTS: Ten patients from six institutions (five USA, one Brazil) were reviewed. Additionally, thirty-one patients were identified in the literature from 1975-2021. Of the 41 total patients, mean age was ten years (range, birth to 35 years); males were predominant (61%). Basal ganglia were the most common tumor location (n=12; 29%), followed by posterior fossa (n=7; 17%). Sixteen patients had non-germinomatous germ cell tumors (NGGCTs) (39%), 14 had pure germinomas (34%), and eight had teratomas (20%); histology was unreported for two (5%). Nine patients (22%) experienced disease relapse, of which four died from tumor progression (one germinoma versus three teratoma). Fifteen patients (37%) experienced treatment-related complications - seven died (four germinoma versus three NGGCT). Of the germinoma patients, two died from chemotherapy-related sepsis, one from post-surgery cardiopulmonary failure, and one from Moyamoya following radiation-therapy (RT) only. Of the NGGCT patients, one died from chemotherapy-related sepsis, one from post-surgical infection, and one from pneumonia following surgery/chemotherapy/RT. Three-year overall survival (OS) was 66% for all histological types - 62% germinoma, 79% for NGGCT, and 53% for teratoma. Three-year OS for patients who received RT or chemotherapy was 71% and 75% respectively. Twenty-seven patients remain alive at latest follow-up (mean follow-up from diagnosis: 46.8 months). CONCLUSIONS: Patients with DS treated for CNS GCTs are at an increased risk of treatment-related adverse events. A different therapeutic approach may need to be considered for this patient population to mitigate treatment-related complications and long-term neurocognitive sequelae.

MEDB-49. Relapsed SHH medulloblastomas in young children. Are there alternatives to full-dose craniospinal irradiation?

BACKGROUND/RATIONAL: Following initial irradiation sparing therapy, many young children with relapsed medulloblastoma can be salvaged with craniospinal irradiation (CSI). However, the interval to relapse is short and neurocognitive sequelae remain a major concern. The contribution of molecular subgrouping may help refine indications and modalities of salvage strategies in this population. METHOD: From a cohort of 151 young children with molecularly characterized relapsed medulloblastoma, subset analysis of the SHH medulloblastoma was conducted to describe the practice of salvage radiotherapy and associated post-relapse survival (PRS). RESULTS: Sixty-seven SHH medulloblastoma patients (46 M0; 54 GTR; 11 non-ND/MBEN) received salvage therapy with curative intent. Before relapse, 54 (80.6%) received conventional chemotherapy (CC), 13 (19.4%) high-dose chemotherapy (HDC), while seven had additional focal radiotherapy (fRT). Median time to relapse was 11.1 months (range 3.8-41.0) and 43.3% were localized. Thirty patients (16 localized relapse) underwent surgery. Forty-seven (71.2%) received salvage radiotherapy (20 with CC; 10 with HDC; 15 alone, two unknown). CSI and fRT accounted for 82% and 18% respectively. CSI median dose was 36Gy (range 18-39Gy). Ten patients (eight with localized relapse) received CSI doses ≤23.4Gy. Nineteen patients (28.8%) did not receive any radiotherapy (nine HDC; 10 CC only). Radiotherapy was associated with better 3-year PRS (73.0% versus 36.1%; p=0.001). All patients treated with CSI ≤ 23.4Gy were alive at median follow-up of 69 months(24-142). Six of nine patients treated with HDC without irradiation were alive at last follow-up. Sixty-three percent of patients received reduced dose CSI(≤23.4Gy), fRT, or no radiotherapy, and their PRS did not significantly differ from those who received CSI ≥ 30.6Gy (p = 0.54). CONCLUSION: While salvage CSI provided PRS benefit in this SHH medulloblastoma cohort, we report the use of reduced salvage radiotherapy and irradiation avoidance in 63% of the patients, with 60% alive at last follow-up.

ETMR-16. Embryonal tumors with multi-layered rosettes: A case series in treatment for newly diagnosed children

BACKGROUND: Embryonal tumors with multi-layered rosettes (ETMRs) are rare pediatric brain tumors with poorly defined prognostic features, standard of care treatments or outcome data. Recent data suggest that high-dose chemotherapy and radiotherapy is correlated with improved survival compared to chemotherapy alone. CASE DESCRIPTIONS: Four patients with newly diagnosed ETMRs were treated with 2 cycles of induction chemotherapy per PBTC-026 using isotretinoin, vorinostat, vincristine, cisplatin, etoposide, cyclophosphamide with added intrathecal topotecan. Second look surgery was performed if not in complete remission (CR). Consolidation was with three cycles of marrow-ablative chemotherapy (carboplatin and thiotepa) with autologous hematopoietic cell rescue followed by focal irradiation and 12 cycles of maintenance chemotherapy with intrathecal topotecan, vorinostat and isotretinoin. Patient 1 was a 3-year-old female with right parietal tumor, localized, and achieved gross total resection (GTR). Patient 2 was an 11-month-old male with posterior fossa tumor, localized, and achieved subtotal resection. Patient 3 was a 9-month-old female with posterior fossa tumor with near GTR, and metastasis to T12/L1 and L3/L4. [DTB1] [HNT2] Patient 4 was a 34-month-old male with a right frontal lobe tumor, localized and achieved GTR. Patient 1 is now 18 months from diagnosis and in CR. Patient 2 had second look surgery both after induction and consolidation but suffered neurologic injury to the brainstem which led family to decline further therapy. He is currently 14 months from diagnosis with stable residual disease. Patient 3 had local disease recurrence following radiation therapy at 10 months post diagnosis[DTB3] [HNT4] , prior to maintenance. Patient 4 remains in CR at 13 months from diagnosis, currently in maintenance with vorinostat and isotretinoin but declined intrathecal topotecan. CONCLUSION: This case series adds to current knowledge of intensive multi-modal therapy for newly diagnosed ETMR. Further study to define standard optimal treatments in this high-risk group of patients is warranted.

HGG-34. Upfront Molecular Targeted Therapy for the Treatment of BRAF-mutant Pediatric High-Grade Glioma

BACKGROUND: The prognosis for pediatric high-grade glioma (pHGG) is poor despite aggressive multi-modal therapy. Objective responses to targeted therapy with BRAF inhibitors have been reported in some patients with recurrent BRAF-mutant pHGG but are rarely sustained. METHODS: We performed a retrospective, multi-institutional review of patients with BRAF-mutant pHGG treated with off-label BRAF +/- MEK inhibitors as part of their initial therapy. RESULTS: Nineteen patients were identified, with a median age of 10.7 years (range: 1.8–20.3). Histologic diagnoses included HGG (n=6), glioblastoma (n=3), anaplastic ganglioglioma (n=4), diffuse midline glioma (n=3), high-grade neuroepithelial tumor (n=1), anaplastic astrocytoma (n=1), and anaplastic astroblastoma (n=1). Recurrent concomitant oncogenic alterations included CDKN2A/B loss, H3 K27M, as well as mutations in ATRX, EGFR and TERT. Eight patients received BRAF inhibitor monotherapy. Eleven patients received combination therapy with BRAF and MEK inhibitors. Most patients tolerated long-term treatment well with no grade 4–5 toxicities. Objective and durable imaging responses were seen in the majority of patients with measurable disease. At a median follow-up of 2.3 years (range,0.3–6.5), three-year progression-free (PFS) and overall survival (OS) for the cohort were 65% and 82%, respectively, and superior to a historical control cohort treated with conventional therapies. CONCLUSIONS: Upfront targeted therapy for patients with BRAF-mutant pHGG is feasible and effective, with superior clinical outcomes observed compared to historical data. This promising treatment paradigm is currently being evaluated prospectively in the Children’s Oncology Group ACNS1723 clinical trial.

Upfront Molecular Targeted Therapy for the Treatment of BRAF-Mutant Pediatric High-Grade Glioma

BACKGROUND

The prognosis for patients with pediatric high-grade glioma (pHGG) is poor despite aggressive multi-modal therapy. Objective responses to targeted therapy with BRAF inhibitors have been reported in some patients with recurrent BRAF-mutant pHGG but are rarely sustained.

METHODS

We performed a retrospective, multi-institutional review of patients with BRAF-mutant pHGG treated with off-label BRAF +/- MEK inhibitors as part of their initial therapy.

RESULTS

Nineteen patients were identified, with a median age of 11.7 years (range, 2.3-21.4). Histologic diagnoses included HGG (n=6), glioblastoma (n=3), anaplastic ganglioglioma (n=4), diffuse midline glioma (n=3), high-grade neuroepithelial tumor (n=1), anaplastic astrocytoma (n=1), and anaplastic astroblastoma (n=1). Recurrent concomitant oncogenic alterations included CDKN2A/B loss, H3 K27M, as well as mutations in ATRX, EGFR and TERT. Eight patients received BRAF inhibitor monotherapy. Eleven patients received combination therapy with BRAF and MEK inhibitors. Most patients tolerated long-term treatment well with no grade 4-5 toxicities. Objective and durable imaging responses were seen in the majority of patients with measurable disease. At a median follow-up of 2.3 years (range, 0.3-6.5), three-year progression-free and overall survival for the cohort were 65% and 82%, respectively, and superior to a historical control cohort of BRAF-mutant pHGG patients treated with conventional therapies.

CONCLUSIONS

Upfront targeted therapy for patients with BRAF-mutant pHGG is feasible and effective, with superior clinical outcomes compared to historical data. This promising treatment paradigm is currently being evaluated prospectively in the Children's Oncology Group ACNS1723 clinical trial.

HGG-37. UPFRONT TARGETED THERAPY FOR THE TREATMENT OF BRAFV600E-MUTANT PEDIATRIC HIGH-GRADE GLIOMA – A MULTI-INSTITUTIONAL EXPERIENCE

Introduction

Sustained responses to molecular targeted therapy with BRAF with or without MEK inhibitors have been reported in patients with recurrent BRAFV600E-mutant pediatric high-grade gliomas (pHGG). The role of upfront targeted therapy in this population, however, has not yet been established.

Methods

We performed a retrospective, multi-institutional record review of patients with BRAFV600E-mutant pHGGs, treated with off-label BRAF and/or MEK inhibitors as part of their initial adjuvant therapy.

Results

Seventeen patients were identified (median age at diagnosis, 8.8 years, range 1.8–20.2). Histologic diagnoses included HGG/glioblastoma (n=10), anaplastic ganglioglioma (n=3), high-grade neuroepithelial tumor (n=2), diffuse midline glioma (n=1) and anaplastic astroblastoma (n=1). Ten patients underwent biopsy (n=8) or subtotal resection (n=2), while near-total or complete resection was accomplished in seven. Concomitant genetic alterations including CDKN2A/B loss, H3K27M and TERT promotor mutations were found in eight tumors. Thirteen patients received focal radiation therapy (RT) and one received craniospinal irradiation prior to targeted therapy. Adjuvant targeted therapy was initiated shortly after diagnosis or completion of RT. Five patients received BRAF-inhibitor monotherapy (dabrafenib or vemurafenib). Twelve patients received combination therapy with the addition of a MEK inhibitor (trametinib). For patients with measurable disease, best responses per COG criteria were CR (n=3), PR (n=7), SD (n=3) and PD (n=1). With median follow-up of 29 months (range 8–78), two-year PFS and OS for the cohort were 74.7% and 81.1%, respectively. Ten (59%) patients remain free of disease recurrence or progression. Grade 3 or higher toxicities were reported in four patients (neutropenia, skin toxicity/photosensitivity, fatigue and weight loss), leading to therapy discontinuation in two.

Conclusions

Upfront targeted therapy for patients with BRAFV600E mutant pHGG appears tolerable and effective, with a durable disease control rate that is superior to historical data. This promising paradigm is currently being evaluated prospectively in the COG ACNS1723 clinical trial.

RARE-21. A RARE CASE OF PEDIATRIC SPINDLE CELL ONCOCYTOMA WITH EML4-ALK FUSION

A 12 year-old male presented with a 2-month history of intermittent headaches, nausea, and vomiting. Magnetic resonance imaging (MRI) of the brain revealed a 2.2 x 3.5 x 2.6 cm lobulated, sellar/suprasellar mass, mildly T1/T2 hyperintense, with mild homogeneous enhancement and diffusion restriction. He underwent transsphenoidal and right craniotomies for gross total resection of the mass. Pathology demonstrated a hypercellular neoplasm with spindled to ovoid tumor cells arranged in fascicles and tight whirls, consistent with a spindle cell oncocytoma. OncoKids, a DNA- and RNA-based next generation sequencing panel, demonstrated an in-frame EML4 exon 2-ALK exon 19 fusion with a total of 179,872 supporting reads. The EML4-ALK fusion gene is predicted to encode a chimeric tyrosine kinase that facilitates multimerization and autophosphorylation of ALK, and activates its downstream targets, such as RAS/ERK, PI3K/AKT, and JAK/STAT pathways. This fusion is found in approximately 5% of patients with non-small cell lung cancer, a subset of inflammatory myofibroblastic tumors, as well as single cases of pulmonary atypical carcinoid, cholangiocarcinoma, and high-grade glioma. However, it has not been previously described in oncocytoma. Chromosomal microarray analysis demonstrated two interstitial non-contiguous deletions in 2p, and an interstitial deletion in 18q that does not include any known cancer-related genes. The deleted segment in 2p23.3p23.2 includes DNMT3A, which mediates DNA methylation and functions in modification of gene expression. DNMT3A mutations are frequent in hematological malignancies, however their role in oncocytoma is currently unknown. The proximal breakpoint of the deletion in 2p23.3p23.2 is in close proximity to but does not reside within ALK. Spindle cell oncocytoma is rarely reported in the pediatric population, with only one case described in the literature. This is the first case report of an oncocytoma with an EML4-ALK fusion. Additional studies are warranted to confirm its functional effect.

Two promoters with distinct activities in different tissues drive the expression of heparanase in Xenopus

In Xenopus laevis embryos, heparanase, the enzyme that degrades heparan sulfate, is synthesized as a preproheparanase (XHpaL) and processed to become enzymatically active (XHpa active). A short nonenzymatic heparanase splice variant (XHpaS) is also expressed. Using immunohistochemistry, Western blot, and heparanase promoter analysis, we studied the dynamic developmental expression of the three heparanases. Our results indicate that (1) all three isoforms are maternally expressed; (2) XHpaS is a developmental variant; (3) in the early embryo, heparanase is localized to both the plasma membrane and the nucleus; (4) several tissues express heparanase, but expression in the developing nervous system is most evident; (5) two promoters with distinct activities in different tissues drive heparanase expression; (6) Oct binding transcription factors may modulate heparanase promoter activity in the early embryo. These data argue that heparanase is expressed widely during development, but localization and levels are finely regulated.

Two heparanase splicing variants with distinct properties are necessary in early Xenopus development

Heparanase is an endoglycosidase that cleaves heparan sulfate (HS) side chains from heparan sulfate proteoglycans (HSPGs) present in extracellular matrix and cell membranes. Although HSPGs have many functions during development, little is known of the role of the enzyme that degrades HS, heparanase. We cloned and characterized the expression of two heparanase splicing variants from Xenopus laevis and studied their function in early embryonic development. The heparanase gene (termed xHpa) spans over 15 kb and consists of at least 12 exons. The long heparanase (XHpaL) cDNA encodes a 531-amino acid protein, whereas the short splicing variant (XHpaS) results in a protein with the same open reading frame but missing 58 amino acids as a consequence of a skipped exon 4. Comparative studies of both isoforms using heterologous expression systems showed: 1) XHpaL is enzymatically active, whereas XHpaS is not; 2) XHpaL and XHpaS interact with heparin and HS; 3) both proteins traffic through the endoplasmic reticulum and Golgi apparatus, but XHpaL is secreted into the medium, whereas XHpaS remains associated with the membrane as a consequence of the loss of three glycosylation sites; 4) overexpression of XHpaS but not XHpaL increases cell adhesion of glioma cells to HS-coated surfaces; 5) XHpaL and XHpaS mRNA and protein levels vary as development progresses; 6) specific antisense knock-down of both XHpaL and XHpaS, but not XHpaL alone, results in failure of embryogenesis to proceed. Interestingly, rescue experiments suggest that the two heparanases regulate the same developmental processes, but via different mechanisms.