Review on Glioma Classification and cIMPACT-NOW updates on WHO 2016 Histological Classification

Abstract

Glioma is a term used to refer to neoplastic proliferation of neuroglial structures like astrocytes, oligodendrocytes and ependymal cells. WHO classification of 2000 and 2007 dealt with cytomorphological and histological features alone to determine and diagnose biological behavior of tumors. Histological criteria like anaplasia, mitosis, microvascular proliferation [MVP] and necrosis could not be used to accurately and reproducibly diagnose the new subtypes and hence the revised WHO 2016 criteria which integrates the molecular and histomorphological criteria has become more widely accepted for classification and grading of gliomas.  The International Society of Neuropathology established the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) in 2016 to facilitate this attempt. Some of the major changes adapted in WHO 2016 are incorporation of genetically defined entities in diffuse gliomas, incorporation of genetically defined ependymoma variant and identifying IDH-wildtype and mutant glioblastoma entities . This review focuses on the newer subtypes introduced in the WHO 2016 with special emphasis on the molecular and the genetic mutational categories of gliomas.