CDKN2B and astrocytoma (excluding glioblastoma): In addition to histological Grade 4 IDH‐mutant astrocytoma, astrocytoma with IDH‐mutations of WHO Grades 2, 3 and homozygous CDKN2A and/or CDKN2B deletions are also defined as astrocytoma, IDH‐mutant, Grade 4, despite their relatively lower histopathology grades.8, 13, 14, 15