PURPOSE: The molecular pathogenesis of pediatric ependymoma remains unclear. Our 
study was designed to identify genetic changes implicated in ependymoma 
progression.
PATIENTS AND METHODS: We characterized 59 ependymoma samples (33 at diagnosis 
and 26 at relapse) using array-comparative genomic hybridization (aCGH). 
Specific chromosomal imbalances were confirmed by fluorescent in situ 
hybridization, and candidate genes were assessed by real-time quantitative 
polymerase chain reaction (qPCR), immunohistochemistry, sequencing, and in vitro 
functional studies.
RESULTS: aCGH analysis revealed a significant increase in genomic imbalances on 
relapse compared with diagnosis, such as gain of 9qter and 1q (54% v 21% and 12% 
v 0%, respectively) and loss of 6q (27% v 6%). Supervised tumor classification 
showed that gain of 9qter was associated with tumor recurrence, age older than 3 
years, and posterior fossa location. Using a candidate-gene strategy, we found 
an overexpression of two potential oncogenes at the locus 9qter: Tenascin-C and 
Notch1. Moreover, Notch pathway analysis (qPCR) revealed overexpression of Notch 
ligands, receptors, and target genes (Hes-1, Hey2, and c-Myc), and 
downregulation of Notch repressor Fbxw7. We confirmed by immunohistochemistry 
the overexpression of Tenascin-C and Hes-1. We detected Notch1 missense 
mutations in 8.3% of the tumors (only in the posterior fossa location and in 
case of 9q33-34 gain). Furthermore, inhibition of Notch pathway with a 
gamma-secretase inhibitor impaired the growth of ependymoma stem cell cultures.
CONCLUSION: The activation of the Notch pathway and Tenascin-C seem to be 
important events in ependymoma progression and may represent future targets for 
therapy. We report, to our knowledge for the first time, recurrent oncogenic 
mutations in pediatric posterior fossa ependymomas.