Actionable FGFR1 and BRAF mutations in adult circumscribed gliomas

Circumscribed gliomas -pilocytic astrocytomas (PA), gangliogliomas (GG), ependymomas (EP)- are mostly low-grade tumours but may progress to anaplasia and sometimes surgery can be challenging due to deep anatomical localization. Because of the high frequency of MAPK-pathway alterations and availability of targeted therapies for FGFR1 and BRAF-mutated tumors, we investigated these mutational hotspots in a cohort of adult circumscribed gliomas.

Adult patients (>15 years) with diagnosis of PA, GG, EP and DNET were retrospectively identified from two institutions databases. Genomic DNA was extracted from formalin-fixed paraffin-embedded or frozen samples and exons including codons 546 and 656 of FGFR1 and V600 of BRAF were sequenced.

FGFR1 mutations were identified in 15/108 PA and were particularly frequent in optic pathway (6/9 vs. 9/108; p = 10^-4). FGFR1 was mutated in 3/75 grade II versus 2/7 grade III GG (p = 0.05), 1/7 DNET, 1/100 EP grade II. We found 3/108 PA with BRAF pVal600Glu and 6/108 with p.Thr599_Val600insThr. The p.Val600Glu was found in 14/75 grade II GG. No EP were BRAF mutated.

We report actionable targets, including frequent FGFR1 mutation in optic-pathway PA that makes them excellent candidates to anti-FGFR therapies, and BRAF non-canonical mutations in PA.