Molecular genetics of pediatric brain stem gliomas. Application of PCR techniques to small and archival brain tumor specimens.

Brain stem gliomas are pediatric astrocytomas that histologically resemble adult supratentorial astrocytomas such as glioblastomas multiforme (GBM). Our molecular genetic studies have suggested that adult GBM can be divided into two genetic subsets: tumors with p53 tumor suppressor gene mutations and chromosome 17p loss that occur more commonly in younger patients; and tumors with epidermal growth factor receptor (EGFR) gene amplification that occur more commonly in older patients. Brain stem gliomas have not been studied since biopsies of these tumors are rare and extremely small. We investigated the molecular genetic composition of seven brain stem glioblastomas (two small biopsies, five autopsies) using polymerase chain reaction (PCR) assays for chromosomal loss, gene mutation and gene amplification. Four cases lost portions of chromosome 17p that included the p53 gene. These four cases and one additional case had mutations in the p53 gene. None of the cases showed amplification of the EGFR gene. Allelic losses of the long arm of chromosome 10 were noted in four cases. These results suggest similarities between pediatric brain stem glioblastomas and those GBM that occur in younger adult patients, and confirm the utility of PCR-based means of studying small and archival brain tumor specimens.