Identification of Gains on 1q and Epidermal Growth Factor Receptor Overexpression as Independent Prognostic Markers in Intracranial Ependymoma

Abstract

Pathogenesis of ependymomas is still poorly understood and molecular markers for risk-adapted patient stratification are not available. Our aim was to screen for novel genomic imbalances and prognostic markers in ependymal tumors. We analyzed 68 sporadic tumors by matrix-based comparative genomic hybridization using DNA microarrays containing >6,400 genomic DNA fragments. Novel recurrent genomic gains were validated by fluorescence in situ hybridization using a tissue microarray consisting of 170 intracranial ependymomas. Candidate genes were also tested for mRNA expression by quantitative real-time PCR, and protein expression was determined by immunohistochemistry on the tissue microarray. Chromosomal gain of 1q correlated with pediatric patients (P = 0.004), intracranial ependymomas (P = 0.05), and tumors of grade III (P = 0.002). Gain of 1q21.1-32.1 was associated with tumor recurrence in intracranial ependymomas (P < 0.001). Furthermore, gain of 1q25 as determined by fluorescence in situ hybridization represented an independent prognostic marker for either recurrence-free survival (P < 0.001) or overall survival (P = 0.003). Recurrent gains at 5p15.33 covering hTERT were validated by immunohistochemistry, and elevated protein levels correlated with adverse prognosis (P = 0.01). In addition to frequent gains and high-level amplification of epidermal growth factor receptor (EGFR) at 7p11.2, immunohistochemistry revealed protein overexpression to be correlated with poor prognosis (P = 0.002). EGFR protein status subdivides intracranial grade II ependymomas into two different risk groups (P = 0.03) as shown by multivariate analysis. Thus, the states of 1q25 and EGFR represent independent prognostic markers for intracranial ependymomas to identify patient subgroups with different risk profiles in further clinical investigations. Moreover, EGFR might serve as therapeutic target for more specific chemotherapy applications.