Pleomorphic Xanthoastrocytoma (PXA)

Overview

Pleomorphic xanthoastrocytoma (PXA) is a rare glial tumor most commonly arising in children and young adults, typically in the cerebral hemispheres (often temporal). It is characterized by a high frequency of BRAF V600E mutations (~70%) or, less commonly, BRAF fusions. WHO grade II (conventional PXA) and grade III (anaplastic PXA) are recognized. BRAF V600E-positive PXA may respond to MEK or BRAF inhibitors.

Cohorts in the corpus

  • mixed_pipseq_2017 — PIPseq pediatric pan-cancer cohort (Columbia University Medical Center), which includes a PXA case among 101 high-risk pediatric patients PMID:28007021.

Recurrent alterations

  • PIPseq cohort: TMEM106B-BRAF fusion identified by RNA-seq in a PXA patient — a MEK-inhibitor target; the fusion drives constitutive BRAF/MAPK activation PMID:28007021.

Subtypes

  • WHO grade II (PXA): classic; better prognosis.
  • WHO grade III (anaplastic PXA): increased mitotic activity; worse prognosis.

Therapeutic landscape

  • BRAF V600E-mutant PXA: BRAF inhibitors (vemurafenib, dabrafenib) alone or with MEK inhibitors (trametinib, cobimetinib).
  • BRAF fusion-driven PXA: MEK inhibitors are indicated (BRAF inhibitors paradoxically activate MAPK in fusion contexts).

Sources

  • PMID:28007021 — Oberg et al. PIPseq pediatric pan-cancer sequencing program (n=101).

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