Correlation of copy number aberrations with clinico-pathological criteria in paediatric glial tumours

Abstract

Glial cell tumours represent the largest group of brain tumours in childhood and include astrocytoma (WHO grades I-IV) and ependymoma (WHO grade II-III). However, little is known about the pathogenesis of these tumours. We have used comparative genomic hybridisation (CGH) to investigate the genetic alterations in 128 tumours from children and young adults (< 30 years of age) comprising 52 ependymoma, including 40 samples that have previously been reported (44 grade II and 8 grade III) and 76 astrocytoma (consisting of 34 grade I, 17 grade II, 7 grade III, and 18 grade IV). Genetic alterations were compared to clinicopathological data such as histology, tumour recurrence, and survival in order to identify potential prognostic markers. In ependymoma, 39% of the tumours had no detectable copy number aberrations (CNAs). In the remaining tumours, the most common regions of gain were 4q (29%), 6q (21%), 1q (17%), and 2q (15%). The most common regions of loss were 22 (29%), 16p (17%), 17p (13%), and 20q (13%). Three regions of high copy number amplification were observed in 3 tumours at 1q24-31 (3 cases), 8q21-23 (3 cases), and 9p (1 case). There was no association between any CNA and histology, tumour recurrence, or length of survival. In contrast, in the astrocytoma group there was a clear association between histology and the presence of CNAs. The pattern of genetic alterations became increasingly complex with tumour grade, and grade IV tumours were more likely to have CNAs than lower grade tumours (p = 0.0502). Overall, the most frequent alterations observed in astrocytoma were gain of 4q (11%), loss 16p (10.5%), and loss 17p (10.5%). However, several CNAs were seen predominantly in grade IV tumours (gain 1q, 2q, 4q, and 5q). Fourteen amplicons were observed in 8 tumours of all grades, of which the most common were localised to 7q31 (4 cases), 8q21-22 (3 cases), 19p (2 cases), 2q (2 cases), and 12q15-21 (2 cases). From this study, it appears that paediatric glial tumours are much more genetically heterogeneous than their adult counterparts, and further molecular investigations are needed to define clinically useful subgroups.