60 Are gangliogliomas in children and adults disorders of nervous system development

INTRODUCTION: Gangliogliomas (GGs) are neuroepithelial tumours of the central nervous system (CNS) composed of mature ganglion cells or a mixed population of ganglion and glial cells. Microarray data of low grade gliomas (LGG) including GGs revealed overexpression of the Dlx2 gene, a homeobox gene essential for interneuron migration and differentiation. We hypothesized that GGs are arrested in development, and began to explore the role of the Dlx2 gene. BRAF rearrangements and BRAF V600E point mutations have been reported in pediatric LGG. METHODS: DLX2 expression was examined in GGs using immunofluorescence (IF) and immunohistochemistry (IHC) labelling of formalin fixed paraffin embedded (FFPE) tissue sections, along with staining of glial and neuronal markers. BRAF mutations were detected using a commercial antibody and/or sequence verification of the DNA extracted from the FFPE blocks. RESULTS: In the Discovery cohort 10/30 were DLX2+ (33.3%) and in the Validation cohort 15/40 were DLX2+ (37.5%). Of these 15 cases, 15 were GFAP+ (100%), 15 were synaptophysin and/or NeuN+ (100%), and 13 were OLIG2+ (86.7%); 6 had a BRAF V600E mutation (40.0%). For the Validation cohort of 40 GGs, 28 were OLIG2+ (70.0%); 13/28 co-expressed DLX2 (46.4%). 18/40 cases had a BRAF V600 mutation(17 V600E, 1 V600G; 45.0%) and 6/18 were DLX2+ (33.3%). CONCLUSIONS: DLX2 is expressed in GGs in both neuronal and glial marker expressing tumour cells. Our results support that GGs arise from CNS progenitors arrested at the neuronal-glial cell fate “decision” point.