Genome analysis and gene expression profiling of neuroblastoma and ganglioneuroblastoma reveal differences between neuroblastic and Schwannian stromal cells

Abstract

Neuroblastic tumours are a group of paediatric cancers with marked morphological heterogeneity. Neuroblastoma (Schwannian stroma-poor) (NB-SP) is composed of undifferentiated neuroblasts. Ganglioneuroblastoma intermixed (Schwannian stroma-rich) (GNBi-SR) is predominantly composed of Schwannian stromal (SS) and neuroblastic (Nb) cells. There are contrasting reports suggesting that SS cells are non-neoplastic. In the present study, laser capture microdissection (LCM) was employed to isolate SS and Nb cells. Chromosome 1p36 deletion and MYCN gene amplification were found to be associated in two out of seven NB-SPs, whereas no abnormalities were observed in five GNBi-SRs. In some cases, loss of heterozygosity (LOH) at 1p36 loci was detected in Nb cells but not in the bulk tumour by LCM; furthermore, LOH was also identified in both SS and tumour tissue of a GNBi-SR. DNA gain and loss studied by comparative genomic hybridization were observed at several chromosome regions in NB-SP but in few regions of GNBi-SR. Finally, gene expression profiles studied using an oligo-microarray technique displayed two distinct signatures: in the first, 32 genes were expressed in NB-SP and in the second, 14 genes were expressed in GNBi-SR. The results show that NB-SP is composed of different morphologically indistinguishable malignant cell clones harbouring cryptic mutations that are detectable only after LCM. The degree of DNA imbalance is higher in NB-SP than in GNBi-SR. However, when the analysis of chromosome 1p36 is performed at the level of microdissection, LOH is also observed in SS cells. These data provide supportive evidence that SS cells have a less aggressive phenotype and play a role in tumour maturation.