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. 2021 Aug 12;3(1):vdab109. doi: 10.1093/noajnl/vdab109

Figure 5.

Figure 5.

Radiation-induced gliomas (RIGs) are genetically distinct from most other astrocytoma and glioma brain tumor types and share the highest number of common genetic alterations with the pedGBM_RTK1 methylation subclass of pediatric glioblastoma. Major recurrent genetic features of RIGs were defined as occurring in more than 40% or cases and are compared here with hallmark genetic features of the indicated WHO-defined CNS tumors65 (colored boxes ordered by increasing similarity to RIG): IDH-mutant anaplastic astrocytoma,65–68,91–93 pilocytic astrocytoma,18,65,71,73–75,91,94 diffuse midline glioma (DMG), H3 K27M-mutant,33,58,65,77–79,81–83 IDH-wild type glioblastoma (GBM).65,85–89 The closest corresponding methylation subclass20,62 is indicated beneath each WHO-defined tumor type in italics. Comparison of recurrent genetic features of RIGs with the pedGBM_RTK1 methylation subclass of pediatric GBM62 is also shown. Being pediatric-specific, this methylation class does not align with a specific entity in the 2016 WHO diagnostic guidelines65 therefore we have used a new entity proposed in the 2021 edition (diffuse pediatric-type high-grade glioma (HGG), H3-wild type and IDH-wild type).95 Common astrocytoma/glioma genetic alterations that were only observed in a small proportion of RIGs (e.g. ATRX mutation (14%), BRAF mutation (10%), BRAF fusion (5%), EGFR amplification (13%), IDH1 mutation (2%), MYCN amplification (10%), PTEN deletion (16%)) were considered infrequent and not deemed to be a defining characteristic of RIG. Asterisk indicates a genetic feature associated only with the GBM, RTK I methylation subclass and has not been described as a feature of GBM, IDH-wild type. Abbreviations for the methylation classes are as previously defined20,62: A IDH—IDH glioma, subclass astrocytoma; LGG, PA PF—low-grade glioma, subclass posterior fossa pilocytic astrocytoma; LGG, PA MID—low-grade glioma, subclass midline pilocytic astrocytoma; DMG K27—diffuse midline glioma H3 K27M mutant; GBM, RTK I—glioblastoma, IDH wild type, subclass RTK I; pedGBM_RTK1—pediatric glioblastoma enriched for PDGFRA amplification.