PTEN and neoplasm: In addition to the combination of mutations, also the cell of origin is a determinant of the brain tumour phenotype: a detailed study identified gliomas (in a GFAP‐Cre‐Nf1; p53; Pten model) originating from cells of the diencephalon and brainstem (i.e. ventral brain) to express Olig2 and PDGFRA, whilst the remaining tumours were more aggressive and showed a higher level of GFAP expression [137].