For IDH mutant astrocytomas, any combination of microvascular proliferation, necrosis (characteristics of anaplastic astrocytomas) or CDKN2A/B homozygous deletion now allows for the diagnosis of Astrocytoma, IDH-mutant, WHO grade 4—note the use of Arabic is now suggested, rather than Roman, numbers [11]. Here, IDH1 is linked to astrocytoma (excluding glioblastoma).