Astroblastoma (ASTB)

Overview

Astroblastoma is a rare CNS/brain neoplasm classified under Miscellaneous Neuroepithelial Tumors (MNET) in OncoTree. A molecularly defined subset is characterised by MN1::BEND2 fusions (the canonical defining alteration for the WHO-recognised “MN1-altered” epigenetic subclass), with EWSR1::BEND2 fusions reported in a small number of cases. The EWSR1::BEND2 variant shows only low-confidence methylation similarity to MN1::BEND2-rearranged astroblastoma (prediction score 0.364 on the brain-tumor classifier), suggesting it may represent an adjacent but distinct entity.

Cohorts in the corpus

  • No dedicated ASTB cohort study in the corpus. Referenced as a comparison entity in a bladder EWSR1::BEND2 sarcoma case report (N=1) PMID:28199314.

Recurrent alterations

  • MN1 — canonical fusion partner in MN1-rearranged astroblastoma; MN1::BEND2 fusions define an epigenetic subtype characterised by a distinct methylation profile. Referenced as the CNS prototype of BEND2-driven neoplasms PMID:28199314.
  • BEND2 — 3’ fusion partner shared across MN1::BEND2 (canonical CNS astroblastoma) and the rare EWSR1::BEND2 variant; contributes its C-terminal BEN domain to the fusion protein. A bladder small round cell sarcoma with EWSR1::BEND2 showed low-confidence methylation similarity (score 0.364) to MN1::BEND2 astroblastoma, with the EWSR1 breakpoint (exon 10) differing from those reported in CNS cases PMID:28199314.
  • EWSR1 — alternative 5’ fusion partner replacing MN1 in rare EWSR1::BEND2 cases; EWSR1 exon 10 fused to BEND2 exon 2 was identified in one bladder sarcoma with methylation-classifier similarity to ASTB PMID:28199314.

Subtypes

  • MN1::BEND2-rearranged astroblastoma — canonical WHO-defined subclass with a distinctive DNA methylation profile and epigenetic class.
  • EWSR1::BEND2 variant — documented in at least one extracranial location (urinary bladder); methylation profile did not match any sarcoma classifier but showed low-confidence similarity to ASTB subclass PMID:28199314.

Therapeutic landscape

  • No targeted therapies for ASTB established in the corpus. Ewing-sarcoma–like chemotherapy protocols have been applied to EWSR1-non-ETS fusion sarcomas misclassified as Ewing sarcoma before molecular characterisation PMID:28199314.

Sources

  • PMID:28199314 — EWSR1::BEND2 bladder sarcoma case with methylation similarity to MN1::BEND2 astroblastoma.

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