Genomic and epigenomic re-categorization of congenital glioblastoma and desmoplastic infantile ganglioglioma.

Abstract

The recently updated World Health Organization classification of central nervous system (CNS)tumors, 5th edition, (CNS5) reclassifies pediatric tumors according to their distinct molecular drivers, recognizing anew entity-infant-type hemispheric glioma (IHG). Defined by its unique epigenetic signature, and/or genomicfusions in ALK, ROS1, NTRK, or MET gene, IHG subsumes many cases previously classified as congenitalglioblastoma (cGBM). Histologic features of IHG are still poorly defined with known overlap with a clinic radiologicallysimilar entity-desmoplastic infantile ganglioglioma/astrocytoma (DIG). We revisited our cohort of cGBMs and DIGs, now reclassifying them according to CNS5 and comparedthe clinical, radiologic, molecular and histologic features between the two. 3/6 cases of cGBM that underwent targeted NGS fusion mutation panel were positive for ALK fusions(involving MAP4, MZT2Bex2, and EML4 genes as fusion partners), and 1/6 showed GOPC:ROS1 fusion.Interestingly, GOPC:ROS1 fusion was also shared by 1/5 cases of histologically defined DIG. DNA methylationprofiling using the Heidelberg classifier (v12.3) recategorized 2/5 DIG cases as IHG (including the case with ROS1alteration). In conclusion, histology alone is insufficient to distinguish IHG from DIG, necessitating epigenomic andgenomic testing for the diagnosis of early-life gliomas.