TP53 mutation is infrequent in aneuploid choroid plexus tumours

Abstract

Choroid plexus tumours are uncommon primary brain tumours that arise predominantly in the paediatric population. Although cytogenetic studies are limited, it appears that in both benign choroid plexus papilloma (WHO grade I) and histologically malignant choroid plexus carcinoma (WHO grade III), there is a prevalence of numerical rather than structural chromosomal aberrations. In particular, additional copies of chromosomes 7, 8, 12, 15, 18, and 20 have been reported in several tumours. In the present study, we analysed 10 choroid plexus tumours comprising 9 papillomas and 1 carcinoma for genomic loss or gain using comparative genomic hybridisation. Four cases had no detectable regions of imbalance. The remaining tumours had multiple copy number aberrations (CNAs) ranging from 2 to 22 (mean 8.2), and all of the autosomes were involved at least once. The most common changes were gains of 7, 9p, and 20, and losses of 3p and 10q, which were each seen in 3 cases. In contrast to previous reports, chromosome loss was as frequent as gain. Additionally, imbalance of single chromosome arms was observed in 3 tumours, which may be indicative of structural abnormalities. In many other tumour types, aneuploidy is often associated with loss of functional p53. To investigate the role of TP53 in the development of choroid plexus tumours, we screened all 10 cases for mutations by direct sequencing of exons 4–8 and their corresponding splice junctions. In 1 papilloma, a missense mutation was detected at codon 273 in which a G to A transition results in the replacement of an arginine residue by a histidine residue. Codon 273 is a hotspot for mutation in many types of tumour, including astrocytoma. Interestingly, this tumour was aneuploid for every autosome. There were no mutations present in the remaining 9 cases, and it is unlikely that TP53 inactivation is critical to the pathogenesis of choroid plexus tumours. Further investigations are necessary to elucidate the genetic pathways involved in tumourigenesis.