The revised fourth edition of the WHO classification of Tumours of the Central Nervous System, published in 2016, comprises several newly recognized tumour entities, and a significant restructuring of the classification, mainly based on genetic profiling. Glioblastomas are now classified into two major types. Isocitrate dehydrogenase (IDH)-wildtype glioblastoma (primary glioblastoma IDH-wildtype) develops rapidly de novo without a recognizable precursor lesion. IDH-mutant glioblastoma (secondary glioblastoma IDH-mutant) develops more slowly through malignant progression from diffuse or anaplastic astrocytoma. Medulloblastomas are now defined by combining histological patterns (classic, desmoplastic/nodular, extensive nodularity, anaplastic) and genetic hallmarks (WNT-activated; SHH-activated, TP53-mutant; SHH-activated, TP53-wildtype; non-WNT/non-SHH). Other newly recognized tumour entities include diffuse midline glioma, H3 K27M-mutant; ependymoma, RELA fusion-positive; and embryonal tumour with multilayered rosettes. The new classification is a significant step forward and will facilitate the development of novel targeted therapies of brain tumours.
The 2007 WHO classification of tumours of the central nervous system
