Posterior fossa (PF) ependymomas are the most common pediatric ependymomas and remain poorly understood. Histological grading does not correlate with clinical outcome or response to standard therapies, highlighting the need to identify new prognostic markers. Recent work identified 2 molecular subclasses, PF group A (PFA) and PF group B (PFB) that differ in methylation phenotype, age of onset, and prognosis.1,2 PFA ependymomas, found predominantly in children, exhibit CpG island hypermethylation and transcriptional silencing of the polycomb recessive complex 2, and carry worse prognosis. Methylation of promoter CpG islands silences gene expression, and PFA ependymomas exhibit repressed expression of differentiation genes. In contrast, PFB ependymomas are found in adults, do not exhibit CpG island hypermethylation, and carry better prognosis. These data suggest that epigenetic dysregulation is important in PF ependymoma pathogenesis, and Bayliss et al3 recently reported further epigenetic characterization of these tumors in Science Translational Medicine.
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