IDH1 and astrocytoma (excluding glioblastoma): Under that classification, approximately 90–95% of grade 4 astrocytoma have no IDH1/2 mutations, while the remaining 5–10% harbor IDH1/2 mutations [4]; however, the latter are now classified as IDH-mutant astrocytoma, WHO grade 4, according to the 2021 World Health Organization (WHO) classification criteria [13,14].