DNA methylation pattern of brain stem pilocytic astrocytomas in children

10021 Background: Pilocytic astrocytoma (WHO grade I) comprises the most frequent brain tumor in childhood. We were recently able to identify BRAF as a centrally important oncogene in these tumors showing duplication or activation in a majority of cases. Although histologically indistinguishable, tumors with brain stem location have a particularly poor prognosis. It is not well established, whether this is due to their close proximity to pivotal anatomic sites or due to distinct biological characteristics. Methods: To identify novel genes involved in astrocytoma pathogenesis, we performed a genome-wide DNA methylation analysis of 78 pilocytic astrocytoma samples from different tumor locations (diencephalic, cerebral, cerebellar, brain stem). BeadChip methylation technology was used to identify genes showing differential promoter methylation among tumors. Two CpG sites were analyzed for each of a total of 14.000 promoters per sample. Clinical and molecular subgroups were compared using Significance Analysi...