When mutations in all three genes were present, infiltrative GBMs with gene expression profiles similar to astrocytes were produced (type 1 tumours), whereas in the context of Nf1−/−; Trp53−/− these type 1 tumours were seen in addition to more circumscribed GBMs with expression profiles reflecting OPCs were observed (type 2 tumours). This evidence concerns the gene TP53 and neoplasm.