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Pleomorphic xanthoastrocytoma (PXA) in its classic manifestation exhibits distinct morphological features and is assigned to CNS WHO grade 2 or grade 3. Distinction from glioblastoma variants and lower grade glial and glioneuronal tumors is a common diagnostic challenge. We compared a morphologically defined set of PXA (histPXA) with an independent set, defined by DNA methylation analysis (mcPXA). HistPXA encompassed 144 tumors all subjected to DNA methylation array analysis. Sixty-two histPXA matched to the methylation class mcPXA. These were combined with the cases that showed the mcPXA signature but had received a histopathological diagnosis other than PXA. This cohort constituted a set of 220 mcPXA. Molecular and clinical parameters were analyzed in these groups. Morphological parameters were analyzed in a subset of tumors with FFPE tissue available. HistPXA revealed considerable heterogeneity in regard to methylation classes, with methylation classes glioblastoma and ganglioglioma being the most frequent mismatches. Similarly, the mcPXA cohort contained tumors of diverse histological diagnoses, with glioblastoma constituting the most frequent mismatch. Subsequent analyses demonstrated the presence of canonical pTERT mutations to be associated with unfavorable prognosis among mcPXA. Based on these data, we consider the tumor type PXA to be histologically more varied than previously assumed. Histological approach to diagnosis will predominantly identify cases with the established archetypical morphology. DNA methylation analysis includes additional tumors in the tumor class PXA that share similar DNA methylation profile but lack the typical morphology of a PXA. DNA methylation analysis also assist in separating other tumor types with morphologic overlap to PXA. Our data suggest the presence of canonical pTERT mutations as a robust indicator for poor prognosis in methylation class PXA., (© 2022. The Author(s).)

Purpose: 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., Methods: 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., Results: 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., Conclusions: 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.

Objective: To characterize the prevalence and prognostic significance of major driver molecular alterations in adult midline diffuse gliomas (MLG)., Methods: Adults with histologically proven MLG diagnosed between 1996 and 2017 were identified from our tumor bank, systematically reviewed, and reclassified according to WHO 2016. Targeted sequencing was performed, including determination of H3F3A , HIST1H3B , TERTp , IDH1/2 , FGFR1 , p16/CDKN2A , and EGFR status., Results: A total of 116 adult patients (M/F 71/45, median age 46.5 years) with MLG (17 cerebellar, 8 spinal, 30 brainstem, 57 thalamic, and 4 diencephalic nonthalamic) were identified. Most patients had high-grade disease at presentation (grade II: 11%, grade III: 15%, grade IV: 75%). Median overall survival was 17.3 months (14.5-23.8 months). Main molecular alterations observed were TERT promoter, H3F3A , and hotspot FGFR1 (N546 and K656) mutations, in 37%, 34%, and 18% of patients, respectively. IDH1 mutations only affected brainstem gliomas (6/24 vs 0/78; p = 7.5 × 10 -5 ), were mostly non-R132H (contrasting with hemispheric gliomas, p = 0.0001), and were associated with longer survival (54 vs 12 months). TERT promoter mutation (9.1 vs 24.2 months), CDKN2A deletion (9.9 vs 23.8 months), and EGFR amplification (4.3 vs 23.8 months) were associated with shorter survival. Of interest, in contrast with pediatric MLG, H3K27M mutations were not associated with worse prognosis (23 vs 15 months)., Conclusions: Patients with adult MLG present with unique clinical and molecular characteristics, differing from their pediatric counterparts. The identification of potentially actionable FGFR1 mutations in a subset of adult MLG highlights the importance of comprehensive genomic analysis in this rare affection., (© 2018 American Academy of Neurology.)