Medulloblastoma is the most common brain tumour in children. Recent advances in therapy have led to dramatic improvements in survival. However, treatment related long-term morbidity is significant and frequently disabling. The biology of medulloblastoma development remains enigmatic. Improved understanding of the biological factors underlying medulloblastoma development is likely to lead to therapies targeted to the mutations causing neoplastic transformation, leaving normal cells intact and effecting a reduction in unwanted treatment effects. The purpose of this research is to use molecular genetic techniques to evaluate in detail the genomic alterations and associated abnormalities in gene expression of a large series of 33 medulloblastomas and 10 supra-tentorial PNETs. Specifically, we intend to identify potential oncogenes and tumour suppressor genes by focusing on regions of the genome that commonly show loss of one allele, homozygous deletion or gain. lnitially we shall use genomic micro-arrays to localize regions with allelic copy number alterations, followed by conventional molecular genetic techniques to identify specific targeted genes. We will also scan the genome for patterns of genetic alterations and determine the clinical significance of any such 'genetic signatures'. Informed consent for this genetic analysis has been given and LREC approval has been obtained for the study.