IDH1 and astrocytoma (excluding glioblastoma): In the World Health Organization (WHO) Classification of Tumors of the Central Nervous System updated in 2021, IDH-mutant diffuse astrocytic tumors were classified as “astrocytoma, IDH-mutant” and graded as 2, 3, or 4 depending on the presence of mitotic activity, nuclear atypia, pleomorphism, necrosis, and microvascular proliferation [1].