Tumor extracellular vesicle RNA profiling predicts treatment response in pediatric diffuse midline glioma.

Detection of reliable markers of therapy response and drug resistance remains a major unmet need in brain cancer, as serial tumor biopsy is often not feasible. This challenge is particularly acute in diffuse midline glioma (DMG), a fatal pediatric brain tumor for which new targeted therapies are entering clinical use, yet tools for real-time molecular analysis of tumor evolution during therapy remain lacking. Here, we demonstrate that plasma tumor-derived extracellular vesicle (EV) profiling provides a minimally invasive and complementary approach for diagnosis and longitudinal molecular monitoring in H3K27M-mutant DMG. Across patient-derived tumor models and clinical plasma samples, EV mRNA levels correlated strongly with parental tumor transcriptomes. EV H3K27M mRNA enabled discrimination of DMG from non-DMG controls, and exploratory EV response-associated mRNAs were linked to radiographic response and progression-free survival in patients receiving ONC201. To enable tumor-selective EV enrichment and multiplexed molecular profiling within a clinically practical workflow, we developed a new integrated platform supporting same-day EV analysis from small plasma volumes. This work represents the first proof-of-concept demonstration of the diagnostic and treatment response relevance of tumor-derived EV RNA in pediatric DMG and establishes a generalizable framework for minimally invasive longitudinal molecular monitoring in diseases where tissue access is inherently limited.