ID #690 Targetable EGFR alterations drive infiltrative disease in paediatric diffuse midline and hemispheric glioma

Certain subgroups of paediatric-type diffuse high-grade gliomas (PDHGG) have highly infiltrative phenotypes spanning multiple anatomical sites and are commonly characterised by EGFR alterations. These include diffuse midline glioma, EGFR-altered (DMG-EGFR), overlapping with bithalamic glioma, and gliomatosis cerebri (GC). Although clinical studies with EGFR inhibitors have not shown substantial benefit, aberrant EGFR signalling may act as a driver of invasive growth in patient populations that could be selected for in future trials. Taking an unbiased approach to mapping EGFR alterations across PDHGG (n = 1487), we observed a mutation frequency of 8.2%, and amplification of 2.7% cases. These alterations were particularly enriched in the DMG-EGFR (32/52, 62%, enriched in exon7 and 20), and pedHGG-RTK2 subgroups (30/66, 45%), with amplifications restricted to pedHGG-RTK2B (5/18, 28%) and strong enrichment of mutations in pedHGG-RTK2A (21/48, 44%, enriched in exon7 and 15). We further established novel patient-derived models of EGFR-altered tumours for preclinical testing in vitro (n = 9) and in vivo (n = 4), with orthotopic PDXs implanted cortically recapitulating the GC infiltrative growth patterns by histology and MRI. Screening a panel of EGFR inhibitors in vitro, we observe the highest degree of single agent potency with afatinib and neratinib, particularly in a model with exon20 mutations. Screening these agents with drug-on screens against a ‘drugs and tools’ library of ∼900 compounds, we observed synergy with multiple chemotypes of FGFR inhibitors, pointing towards novel combinatorial therapies. Using in utero electroporation of day E12.5/13.5 embryos, addition of EGFR_A289V mutations accelerated tumour growth of both hemispheric TP53/PTEN/NF1 and midline H3.1K27M/EZHIP/TP53 mutant models, representing the first putative genetically engineered models of DMG-EGFR. By integrating molecular genetics, in vivo modelling, and pharmacological validation, this work suggests a role of EGFR-alterations in promoting diffuse infiltrative growth and co-inhibition of FGFR as an actionable vulnerability in EGFR-altered gliomas, addressing an urgent unmet need in paediatric neuro-oncology.