BIOM-49. FGFR ALTERATIONS IN GLIOMAS; CLINICAL, RADIOGRAPHIC AND MOLECULAR CHARACTERIZATION

Abstract

Abstract BACKGROUND FGFR-TACC is the most prevalent type of gene fusion in adult gliomas. It is present in 3-6% of IDH WT (wild-type) gliomas. Due to their histopathological and molecular features, it has been suggested that FGFR3-TACC3 fusions (F3T3) gliomas represent a unique entity among IDH WT gliomas. F3T3 are potent oncogenes that confer sensitivity to FGFR inhibitors. Preliminary data showed promising results of these alterations as actionable targets by FGFR inhibitors. METHODS We retrospectively analyzed molecular data on 912 glioma patients treated at our institution from 2014 to 2023. RESULTS We identified 22 gliomas (2.5%) with FGFR alterations. Median age was 60 years, 14 were female. 14 patients (64%) self-identified as Hispanic. 18 had a diagnosis of glioblastoma, 3 had other gliomas, and one had a low-grade neuroepithelial neoplasm. Ten patients had tumor location in the temporal lobe, 6 frontal, 5 parietal, 3 occipital, 1 multifocal, and 1 basal ganglia. 19 patients had enhancing tumors, while three were non-enhancing. The most common FGFR alteration was FGFR3-TACC3 fusion in 14/22 patients, 6 had FGFR mutations (either single base or amino acid substitutions), one had FGFR-LMNB2 fusion, and one had FGFR3 amplification. 86.4% of our patient cohort (19/22) had a confirmed TERT promoter mutation, while 100% of GBM patients with known TERT promoter status had an associated TERT promoter mutation. 10/22 had CDKN2A/B alterations. One patient had pathology-proven systemic metastases. CONCLUSIONS FGFR3-TACC3 fusions (F3T3) gliomas represent a unique entity among IDH WT gliomas. In our cohort, 100% of the patients with F3T3-positive glioblastomas also had an associated TERT promoter mutation. To our knowledge, this is one of the larger cohorts showing the association between FGFR3 and TERT promoter alterations in glioblastomas. RESULTS will be validated through the upcoming clinical trial ETCTN 10559, including tumor evolution and mechanisms of resistance.