Diffuse midline glioma with novel, potentially targetable, FGFR2-VPS35 fusion.

We report a case of a slow-growing, diffuse, infiltrating glioma in the right brainstem of an 9 year-old boy. The tumor was negative by immunohistochemical staining for histone H3 K27M, BRAF V600E, and IDH1 R132H mutations. Fluorescence in situ hybridization did not reveal a BRAF duplication. Genomic profiling of the tumor, by DNA methylation array and cancer whole exome and transcriptome sequencing, was performed. This analysis showed copy number alterations, including gains of several chromosomes. In addition, a novel fusion involving the first 17 exons of FGFR2 fused to exon 2 of VPS35 was identified. This novel fusion is predicted to result in activation of FGFR signaling, and is potentially targetable using FGFR inhibitors. This tumor expands the spectrum of pediatric diffuse gliomas.