EPEN-42. MOLECULAR PROFILING REVEALS DISTINCT SUBGROUPS OF PEDIATRIC SPINAL EPENDYMOMA

Paediatric spinal ependymomas are important, albeit uncommon, malignant central nervous system tumours. Unlike adults, children with these tumours are likely to experience a more aggressive disease course, with a higher rate of local failure and a higher rate of metastases. The clinical and molecular factors underlying these differences remain poorly characterized. We analyzed spinal ependymoma (SEPN) tumour samples from 27 paediatric patients (female: 11, male: 15; age range: 4–18 years) using genome-wide DNA methylation profiling, copy-number analysis, as well as transcriptome profiling. Using DNA methylation profiles, two distinct unsupervised consensus-clustering approaches, hierarchical clustering and non-negative matrix factorization reliably identified two subgroups. These subgroups were designated as Myxopapillary ependymomas (SP-MPE) and spinal ependymomas (SP-EPN) based on the online Classifier tool (MNP2.0). The genome-wide copy-number analysis showed differences in numbers and pattern of copy-number alterations between these groups. The gain of chromosome 20 (39%) followed by loss of chromosomes 6 (28%), 10 (28%), and 13 (28%) were detected in the SP-MPE group, whereas loss of chromosome 22 was frequent (60%) in the SP-EPN group. Transcriptomics analysis showed that genes associated with oxidative phosphorylation, TCA cycle components, electron transport, and Interferon-gamma production characterize the SP-MPE group whereas potassium ion import and regulation of astrocyte differentiation characterize the SP-EPN group. Western blot analysis validated the increased protein expression of oxidative phosphorylation complexes in SP-MPE. With this study, we provide a foundation for further molecular characterization of pediatric SEPN subgroups. Our results suggest that mitochondrial oxidative phosphorylation may drive the regulation of energy metabolism of SP-MPE tumours.