The evolution of WHO Classification of Tumors of the Central Nervous System from 1979 to 2021

In this article, we look back on history of the classification of tumors of central nervous system (CNS) in brief, and further review the evolution of WHO Classification of Tumors of CNS from the first edition to the fifth edition (WHO CNS5), including the category frame, tumor type/subtype and tumor grading. Changed from histology based classification into more biologically and molecularly defined entities, WHO CNS5 was recently released as expected, after attempt in WHO CNS4 updated version and 7 update publications upon the work of the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy ⁃ Not Official WHO (cIMPACT ⁃ NOW). One of the important changes in WHO CNS5 is the separating gliomas into pediatric ⁃ type and adult ⁃ type based on their well ⁃ established molecular genetic differences. Tracing alone the clue in WHO CNS5, we introduce evolutionary process of entities and subtypes under each categories, and try to explain why they were added, deleted or why their naming was changed from WHO CNS1 to WHO CNS5. Tumor grading in WHO CNS5 has make efforts on moving close to how grading is done for non⁃CNS neoplasms, and added molecular parameters as biomarkers of grading based on histological features. WHO CNS5 has set new standers for clinical management of CNS tumors, and has been expected to facilitate related clinical studies and basic research in the future