World Health Organization Classification of Central Nervous System Tumours, 5th Edition:Points of the Update and the Current Status

Abstract

The World Health Organization Classification of the Tumours, 5th Edition Central Nervous System Tumours(WHO CNS5), has undergone ground-breaking changes in collaboration with cIMPACT-NOW(the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy). Tumors are now classified and named according to the tumor type alone, and the tumor grading is defined within each tumor type. CNS WHO grading is based on either histological or molecular criteria. WHO CNS5 promotes the molecular finding-based classification system and diagnostic criteria, including DNA methylation-based molecular classification. In particular, the classification and CNS WHO grades have extensively been restructured for gliomas. Adult gliomas are now classified into three tumor types according to the IDH and 1p/19q status. Diffuse gliomas with morphological features of glioblastoma and IDH mutation are no longer classified as glioblastoma, IDH-mutant, but as astrocytoma, IDH-mutant, CNS WHO grade 4. Diffuse gliomas without IDH mutation but with molecular features of glioblastoma are classified as glioblastoma, IDH-wildtype. Pediatric-type gliomas are classified separately from adult-type gliomas. Although the shift toward the molecular classification is inevitable, the current WHO classification system has limitations. WHO CNS5 should be regarded as an intermediate stage toward further refined, better structured classification systems in the future.