IDH1 and astrocytoma (excluding glioblastoma): The absence of an IDH mutation is a key characteristic of primary glioblastoma (CNS WHO grade 4), and histological WHO grade 2/3 IDH-wildtype (WT) astrocytomas of the same molecular signature are deemed to represent early glioblastoma stages that can share histological appearances with IDH-mutant astrocytomas [5,6].