The majority of diffuse midline
gliomas, H3 K27-altered (DMG-H3 K27-a), are infiltrating pediatric
brain tumors that arise in the pons with no effective treatment. To understand how clonal evolution contributes to the
tumor's invasive spread, we performed exome sequencing and SNP array profiling on 49 multi-region autopsy samples from 11 patients with pontine DMG-H3 K27-a enrolled in a phase I clinical trial of PDGFR inhibitor
crenolanib. For each patient, a phylogenetic tree was constructed by testing multiple possible clonal evolution models to select the one consistent with somatic mutations and copy number variations across all
tumor regions. The tree was then used to deconvolute subclonal composition and prevalence at each
tumor region to study convergent evolution and invasion patterns. Somatic variants in the PI3K pathway, a late event, are enriched in our cohort, affecting 70% of patients. Convergent evolution of PI3K at distinct phylogenetic branches was detected in 40% of the patients. 24 (~ 50%) of
tumor regions were occupied by subclones of mixed lineages with varying molecular ages, indicating multiple waves of invasion across the pons and extrapontine. Subclones harboring a PDGFRA amplicon, including one that amplified a PDGRFAY849C mutant allele, were detected in four patients; their presence in extrapontine
tumor and normal brain samples imply their involvement in extrapontine invasion. Our study expands the current knowledge on
tumor invasion patterns in DMG-H3 K27-a, which may inform the design of future clinical trials.