[The 2021 WHO Classification of Tumors, 5th edition, Central Nervous System Tumors: A Short Review].

The 2021 WHO classification of tumors of the central nervous system, 5th edition (WHO CNS 5) is built on the previous, revised 4th edition, published in 2016, which incorporated molecular information into the diagnosis of brain tumors for the first time, breaking with the century-old histogenetic classification. WHO CNS 5 also adopted a series of recommendations of "the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT)" that facilitates a consensus review of novel diagnostically relevant data and determines how such information can be fit into future CNS tumor classifications. In WHO CNS 5, the grading system was reformed to "grading within tumor types," and the tumor groups, especially diffuse gliomas, have been significantly restructured; the diffuse gliomas have been divided into the adult type and the pediatric type, the latter being subdivided into low-grade and high-grade gliomas. Based on molecular alterations, 22 novel tumor types are recognized, and some nomenclature has also been revised. The integrated, layered diagnosis of combining histology, grading, and molecular information was recommended to provide clinically relevant information.