The fifth edition of the WHO classification of tumors of the central nervous system (CNS) [
17], published in 2021, has become more reliant on molecular testing for the diagnosis and grading of diffuse gliomas, compared to the 2016 WHO revised 4th edition [
6,
9] that adopted molecular information to define tumor entities for the first time. Under the 2021 revision, only three primary tumor types remained in the group of diffuse gliomas in adults (termed “adult-type diffuse gliomas”), namely, “astrocytoma, IDH-mutant,” “oligodendroglioma, IDH-mutant and 1p/19q codeleted,” and “glioblastoma, IDH-wildtype,” all of which are solely defined by canonical molecular alterations regardless of morphological features. …