Whilst GBM is characterised by isocitrate dehydrogenase wild-type status, the presence of isocitrate dehydrogenase mutation characterises WHO grade 4 astrocytoma which typically results in a less aggressive disease, with a more favourable prognosis, and an increase in both overall and progression-free survival (relative to isocitrate dehydrogenase wild-type tumours)[23]. This evidence concerns the gene IDH3A and astrocytoma (excluding glioblastoma).