Abstract 5719: Clinical response to the PDGFRα inhibitor avapritinib in high-grade glioma patients

PDGFRA has been shown to be commonly altered in high-grade gliomas (HGGs), including histone 3 lysine 27-mutated diffuse midline gliomas (H3K27M DMG), a disease with almost no long-term survivors. Here, we performed comprehensive genomic and transcriptomic analysis of 260 high-grade glioma cases, which revealed PDGFRA genomic alterations (mutations and/or amplifications) in 13% of patients. H3K27M DMGs had significantly higher PDGFRA expression compared to H3 wild-type tumors, and PDGFRA gene amplification resulted in even higher expression levels in H3K27M DMGs as well as H3 wild-type HGGs. We tested a panel of patient- derived pHGG/H3K27M DMG models against a range of PDGFRA inhibitors, including avapritinib, a potent small molecule inhibitor with relatively selective activity against both wild-type and mutant PDGFRA. Avapritinib showed supra-micromolar blood-brain barrier penetration in our pre-clinical models and demonstrated significant survival impact in an aggressive patient-derived H3K27M DMG mouse xenograft model. Finally, building on this preclinical activity, we report here the first clinical experience using avapritinib in eight pediatric and young adult patients with high-grade glioma (H3K27M DMG and/or PDGFRA altered). Avapritinib has thus far been well tolerated with no significant acute toxicities. Most importantly, our preliminary data reveal radiographic response evaluated by RAPNO criteria in 50% of patients, a striking outcome rarely seen in this patient population. In summary, we report that avapritinib is a selective, CNS-penetrant small molecule inhibitor of PDGFRA that shows potent activity in preclinical models and produces promising clinical responses with good tolerability in patients with high-grade glioma. This suggests a promising role for avapritinib therapy in this population with previously dismal outcomes.

Citation Format: Lisa Mayr, Maria Trissal, Kallen Schwark, Jenna Labelle, Andrew Groves, Julia Furtner-Srajer, Jeffrey Supko, Liesa Weiler-Wichtl, Olivia Hack, Jacob Rozowsky, Joana G. Marques, Eshini Pandatharatna, Ulrike Leiss, Verena Rosenmayr, Frank Dubois, Noah F. Greenwald, Sibylle Madlener, Armin S. Guntner, Hana Pálová, Natalia Stepien, Daniela Lötsch-Gojo, Christian Dorfer, Karin Dieckmann, Andreas Peyrl, Amedeo A. Azizi, Alicia Baumgartner, Ondřej Slabý, Petra Pokorná, Pratiti Bandopadhayay, Rameen Beroukhim, Keith Ligon, Christof Kramm, Annika Bronsema, Simon Bailey, Ana Guerreiro Stücklin, Sabine Mueller, David T. Jones, Natalie Jäger, Jaroslav Štěrba, Leonhard Müllauer, Christine Haberler, Chandan Kumar-Sinha, Arul Chinnaiyan, Rajen Mody, Mary Skrypek, Nina Martinez, Daniel C. Bowers, Carl Koschmann, Johannes Gojo, Mariella Filbin. Clinical response to the PDGFRα inhibitor avapritinib in high-grade glioma patients. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5719.

OTHR-46. Single institution experience using molecular analysis of pediatric CNS tumors

Molecular analysis of pediatric CNS tumors helps confirm the diagnosis, but can also guide treatment by identifying prognostic factors allowing for treatment stratification, and by unveiling active signaling pathways which can be targeted. This report is a retrospective review of the molecular analysis performed on all CNS tumors biopsied or resected at Children’s Minnesota over the last 3 years to evaluate our current practices. From 2019-2021, 118 patients with newly diagnosed CNS tumors underwent surgery followed by molecular assessment (14 IHC/FISH, 85 NGS, 7 methylation profiling) on 100% of medulloblastoma, other embryonal tumors, and schwannoma; 90% of ependymoma; 88% of HGG; 71% of LGG/glioneuronal/neuronal tumors; and 50% of meningioma and craniopharygioma. MAPK pathway alterations were seen in 84% of LGG/glioneuronal/neuronal tumors, with KIAA1540-BRAF fusion seen exclusively in pilocytic astrocytoma and BRAFV600E alterations seen in diffuse LGG (75%), PLNTY and PXA. Frequent alterations seen in HGG included H3F3A-K27M, H3F3A-G34, TP53, PDGFRA, ATRX, CDKN2A/B. Common gene alterations in medulloblastoma included monosomy 6 (100%) and alteration of CTNNB1 (50%) in WNT subgroup; PTCH1 (75%) in SHH subgroup; MYC/MYCN gain (60%) or amplification (60%) in Non-WNT/SHH subgroup. Alterations in FOXR2 in CNS neuroblastoma, SMARCB1 in ATRT and C19MC in ETMR confirmed these diagnoses. Supratentorial ependymoma showed ZFTQ-RELA fusion (100%) and infratentorial ependymoma showed chromosomal copy number changes including 1q gain (40%). Meningiomas showed deletion of NF2 and SMARCB1 and craniopharyngioma had alterations in CTNNB1. Molecular analysis confirmed the diagnosis in 23% of tumors, aided with targeted treatment in 20% of patients (82% of HGG, 9% of LGG, 13% of medulloblastomas) and allowed for risk-adapted treatment in 93% of medulloblastomas. These findings indicate that identification of pathogenic variants in CNS tumors aids in the diagnosis and treatment of pediatric CNS tumors and should be considered standard practice.

LGG-63 MEK inhibitor-associated retinopathy (MEKAR) in a pediatric patient with an optic pathway glioma

Pediatric low-grade glioma (LGG) and plexiform neurofibroma (PN) universally have up-regulation of the RAS-mitogen-activated protein kinase (MAPK) pathway. Recent phase I and II clinical trials evaluating MEK inhibitors for the treatment pediatric LGG and PN report efficacy and tolerable side effects, including no reported ophthalmologic toxicity. Contrary to the pediatric experience, adult trials using MEK inhibitors describe several ophthalmologic side effects, including MEK inhibitor-associated retinopathy (MEKAR), also termed central serous-like retinopathy. MEKAR is defined as accumulation of subretinal fluid. It occurs in up to 90% of adults on MEK inhibitors, usually causing minimal to no symptoms, and typically resolving without MEK inhibitor dose adjustment. We report a case of MEKAR in a 15 year old boy with an optic pathway pilocytic astrocytoma with duplication of BRAF (7q34). Baseline ophthalmic exam showed 20/20 vision in his right eye with loss of the temporal hemifield and no light perception vision in the left eye. Nine months into treatment with Selumetinib his ophthalmologic exam and optical coherence tomography (OCT) showed asymptomatic bilateral subretinal fluid. Selumetinib was held for 2 weeks resulting in resolution of the subretinal fluid. Selumetib was resumed at the prior dose and MEKAR recurred 2 weeks later but then permanently resolved 4 weeks later despite remaining on Selumetib. Review of the literature discovered a single publication of 2 pediatric patients with optic pathway glioma who developed MEKAR around 6-7 months after initiating Selumetinib, which resolved after stopping Selumetinib. One patient was symptomatic and despite resolution of symptoms, Selumetinib was not resumed. The other patient was asymptomatic and resumed Selumetib, but redeveloped MEKAR 8 months after restarting Selumetinib. Based on adult experience and the limited pediatric experience outlined above, we recommend pediatric patients with asymptomatic and mild-moderate symptomatic MEKAR undergo close monitoring without Selumetinib dose interruption or modification unless symptoms progress.

LGG-36. DESMOPLASTIC INFANTILE GANGLIOGLIOMA (DIG) WITH A PPP1CB-ALK FUSION IN A 6-YEAR-OLD GIRL

Desmoplastic infantile astrocytoma (DIA) and desmoplastic infantile ganglioglioma (DIG) are benign glioneuronal tumors that typically occur in infants, involve the superficial cerebral cortex, and have an excellent prognosis. DIA/DIG are a distinct molecular entity based on DNA methylation profiling. BRAF600 mutations are frequently reported in DIG/DIA. A recent comprehensive genetic analysis of infantile hemispheric gliomas identified 2 unique groups: group 1 harbored alterations in the receptor tyrosine kinase (RTK) genes ALK, ROS1, NTRK, and MET and group 2 harbored alterations in the RAS/MAPK pathway. We report a case of a 6.5-year-old girl who presented with seizures and right homonymous hemianopia. MRI of her brain demonstrated a large cystic/solid left hemispheric mass with remodelling of the overlying skull, consistent with a long-standing process. She underwent a gross total resection (GTR) and pathology demonstrated a DIG with a PPP1CB-ALK gene fusion (exon 5 to exon 20) identified by RNA sequencing. She remains disease free 12 months following GTR. A literature review identified 4 reported cases of pediatric brain tumors with PPP1CB-ALK gene fusions including: a 3-month-old with a hemispheric high-grade glioma which recurred 4 years later and pathology showed mature ganglioglioma, with both tumors showing the identical PPP1CB-ALK gene fusion; a 10-month-old infant with a hemispheric low-grade glioma; an infant with a “congenital” hemispheric high-grade glioma; and a child with an astrocytoma with no further clinical data. PPP1CB-ALK gene fusion appears to be a rare oncogenic driver in gliomas of infancy, including DIG.

Pilomyxoid astrocytoma treated successfully with vemurafenib

The BRAF V600E missense mutation is known to be present in a subset of central nervous system tumors. We report a patient with a BRAF V600E mutated pilomyxoid astrocytoma who failed multiple conventional chemotherapy regimens. Treatment with vemurafenib, a molecularly targeted therapy against the mutant BRAF V600E kinase, combined with vinblastine resulted in tumor regression. Furthermore, this patient experienced almost immediate progression of disease after holding vemurafenib for only 2-3 weeks, suggesting that the tumor response is vemurafenib dependent. This population of patients may benefit from targeted therapy and testing of individual tumors for BRAF mutations is justified.