IDH1 and glioblastoma: While only ~ 10% of glioblastoma (GBM) of WHO grade IV (current nomenclature is WHO grade IV diffuse glioma) are IDH‐mutant [12], they are particularly enriched in secondary diffuse glioma grade IV (73% vs. 3.7%), suggesting malignant transformation of a lower‐grade primary IDH‐mutant gliomas [11].