TAMI-32. TEMPOROSPATIAL INVASION AND GENETIC EVOLUTION FROM INFRATENTORIAL TO SUPRATENTORIAL COMPARTMENT IN DIFFUSE MIDLINE GLIOMA

Abstract

Abstract Diffuse midline gliomas (DMGs) are very aggressive pediatric brain tumors with dismal prognosis due to therapy-resistant tumor growth and invasion. We performed the first integrated histologic/genomic/proteomic analysis of 21 tumor foci from three pontine DMG cases with supratentorial dissemination. Histone H3.3 K27M was the driver mutation, usually at high variant allele fraction due to recurrent chromosome 1q copy number gain, in combination with germline variants in ATM, FANCM and MYCN genes. Both previously reported and novel recurrent copy number variations and somatic pathogenic mutations in chromatin remodeling, DNA damage response and PI3K/MAPK growth pathways were variably detected, either in multiple or isolated foci. Proteomic analysis showed global upregulation of histone H3, lack of K27 tri-methylation, and further impairment of polycomb repressive complex 2 by ASXL1 downregulation. Activation of oncogenic pathways resulted from combined upregulation of N-Myc, SOX2, p65/p50 NF-kB and STAT3 transcription factors, EGFR, FGFR2, PDGFRa/b and MET receptor tyrosine kinases, and downregulation of PHLPP1/2, PTEN and p16/INK4A tumor suppressors. Upregulation of SMAD4, PAI-1, CD44, and c-Src in multiple foci most likely contributed to invasiveness. This integrated comprehensive analysis allowed spatiotemporal modeling of tumor progression and identified two general pathways of supratentorial invasion, and a multitude of migratory subpopulations within the infratentorial compartment. It also delineated common signaling pathways and potential therapeutic targets, revealing an unsuspected activation of a multitude of oncogenic pathways that may explain the resistance of DMG to current therapies.