Histological features in pediatric central nervous system tumors with FGFR alterations

Introduction
Identification of genetic alterations in central nervous system (CNS) tumors provides diagnostic and prognostic information and allows identification of potential therapeutic targets. Next-generation sequencing (NGS) technologies currently used for molecular testing are costly and remain largely limited to major academic centers or reference labs. Identification of histologic or immunohistochemical correlates for particular molecular alterations can serve as surrogates and can help triage cases for subsequent NGS-based confirmation. Recently, adult IDH-wildtype adult glioblastomas (GBMs) with fibroblast growth factor receptor (FGFR) gene alterations were reported to show palisading monomorphic cells, delicate arcuate vasculature, and microcalcifications. We explored whether pediatric tumors with FGFR fusion also show these histologic features and whether these features could predict the presence of this gene alteration.

Material and methods
We reviewed pediatric CNS tumors with FGFR-fusions to retrospectively determine the presence/absence of the above-mentioned histological features in fusion-positive tumors.

Results
10 pediatric tumors with FGFR fusions were identified. Pediatric tumors demonstrated histologic and tumor type diversity, with diagnoses of pilocytic/pilomyxoid astrocytoma, pediatric-type oligodendroglioma, anaplastic astrocytoma, polymorphous low-grade neuroepithelial tumor of the young, rosette-forming glioneuronal tumor, and extraventricular neurocytoma.

Conclusions
Pediatric FGFR-fused CNS tumors demonstrate histologic features similar to their adult counterparts but also exhibit significant morphologic variability. As such, this histologic variability prevents the prediction of FGFR fusion and necessitates molecular testing for the identification of this alteration.