Abstract
Adult diffuse gliomas with FGFR3-TACC3 (F3T3) fusion are rare and highly heterogeneous central nervous system (CNS) tumors. Current research on the biological behavior of these tumors is limited, especially regarding whether histopathologically low-grade tumors are indolent or represent early-stage high-grade tumors, thereby posing challenges for grading. In this single-center study of 17 patients with adult F3T3 fusion diffuse gliomas (F3T3 gliomas), both low- and high-grade F3T3 gliomas presented distinctive recurrent histopathological features, such as oligodendrocyte-like cells, branched vessels and frequent calcifications. Molecularly, TERT promoter mutations and 7+/10- chromosomal alterations were common; one patient with recurrent glioma with histopathological features of polymorphous low-grade neuroepithelial tumor of the young (PLNTY) had additional CDK4 and MDM2 amplifications. Methylation profiling of 3 samples revealed varied results. A patient whose tumor had histopathological features consistent with PLNTY and a methylation subtype classified as the mesenchymal subtype of glioblastoma (GBM) experienced tumor recurrence 8 months after surgery. After 5-62 months of follow-up, seven patients relapsed, and six died; the primary tumors of the three patients with recurrence presented histopathological characteristics of low-grade glioma (LGG). GBM patients had worse overall survival than LGG patients (p = 0.035) but similar progression-free survival (p = 0.47), indicating that LGG patients may experience recurrence. For adults with tumors with histopathological features of PLNTY, further molecular and methylation analyses are needed for grading. If TERT promoter mutations are present, even with a PLNTY methylation profile, these tumors can still exhibit the biological behavior of high-grade gliomas.