Abstract #18

Presenter

Dr. Andrew Gao is a neuropathologist at University Health Network and Assistant Professor in the Department of Laboratory Medicine and Pathobiology, University of Toronto. He is currently the Program Director of the neuropathology residency program at the University of Toronto.

Authors

Andrew F. Gao¹, José-Mario Capo-Chichi², Adam Smith², Gelareh Zadeh³, Lili-Naz Hazrati⁴, Cynthia Hawkins⁴, Phedias Diamandis¹

¹Division of Anatomic Pathology, Laboratory Medicine Program, University Health Network, Toronto, ON

²Division of Clinical Laboratory Genetics, Laboratory Medicine Program, University Health Network, Toronto, ON

³Division of Neurosurgery, Krembil Neuroscience Program, University Health Network, Toronto, ON

⁴Dept. of Pediatric Laboratory Medicine, Hospital for Sick Children, Toronto, ON

CanMEDS:
Medical Expert (the integrating role), Collaborator, Scholar

Pediatric-type gliomas in adults: pathologic and molecular features

Abstract

The 2021 WHO classification of CNS tumours recognizes adult- and pediatric-type gliomas, which have important clinical and biological differences. While pediatric-type gliomas occur most commonly in children, their frequency and pathologic and molecular features in the general adult population have not been well studied.

We prospectively characterized a single-institution cohort of 498 consecutive gliomas (diffuse gliomas, circumscribed gliomas, and glioneuronal tumours) using immunohistochemistry, Sanger sequencing, panel-based NGS, FISH, SNP array, and/or DNA methylation profiling.

Of 490 cases that could be evaluated (median age 58, range 18-91), pediatric-type alterations were identified in 61 (12%, median age 34, range 18-73). Excluding patients >55yo with glioblastoma (for whom no molecular testing was performed; n=227, 46%), pediatric-type alterations comprised 23% of the remaining cohort (61/263), compared to 45% for IDH mutations, and 32% for adult-type GBM. The frequency of pediatric-type alterations exceeded that of non-canonical IDH mutations in histologic GBMs ≤55yo (8% vs 3%, n=96), and exceeded both non-canonical IDH mutations and adult-type GBM in tumours with diffuse lower-grade histology (20% vs 8% and 17%, respectively, n=138). H3-3A, BRAF, NF1, and mismatch repair were the most commonly altered genes in pediatric-type diffuse high-grade gliomas, while BRAF, FGFR1, and FGFR2 alterations prevailed in diffuse low-grade gliomas, circumscribed gliomas, and glioneuronal tumours.

In our cohort of adult patients, pediatric-type alterations are relatively common, especially in younger adults and lower-grade tumours. Pediatric-type alterations should be routinely included in the diagnostic evaluation and molecular testing of gliomas in adults.