WHO 2016 classification: changes and advancements in the diagnosis of miscellaneous primary CNS tumours

• Published in: Neuropathology and applied neurobiology 2018-02, Vol.44 (2), p.163-171
• Main Authors: Sahm, F., Reuss, D. E., Giannini, C.
• Format: Article
• Language: English
• Subjects: Brain cancer; Brain tumors; Central nervous system; Central Nervous System Neoplasms - classification; Central Nervous System Neoplasms - diagnosis; Central Nervous System Neoplasms - pathology; Classification; craniopharyngioma; Glial cells; Histiocytosis; Humans; Langerhans cell histiocytosis; Lymphoma; melanocytic tumours; Meningioma; Mesenchyme; Mutation; Neoplasia; Neurofibromin 1; peripheral nerve sheath tumours; Pituitary (posterior); Pituitary gland; pituitary tumours; solitary fibrous tumour/haemangiopericytoma; Stat6 protein; Tumors; WHO classification; World Health Organization
• ISSN: 0305-1846; 1365-2990
• DOI: 10.1111/nan.12397

This short review highlights significant changes and recent findings incorporated to varying extent in the WHO 2016 definition of a variety of tumours, including peripheral nerve sheath tumours, meningiomas, mesenchymal nonmeningothelial tumours, melanocytic tumours, lymphomas and histiocytic tumours, germ cell tumours and non‐neuroendocrine pituitary tumours. Most notable classification changes include: adding ‘hybrid nerve sheath tumours’ to the spectrum of benign nerve sheath tumours; an updated definition of atypical meningioma (WHO grade II), including cases with brain invasion; recognizing dural solitary fibrous tumour (SFT) and haemangiopericytoma (HPC) as a single tumour entity characterized by NAB2 and STAT6 gene fusions for which the term SFT/HPC was chosen; recognizing that pituitary granular cell tumour, spindle cell oncocytoma, and pituicytoma all share nuclear expression of TTF‐1, possibly representing a spectrum of a single nosological entity derived from posterior pituitary glial cells. The most significant diagnostic markers which have emerged include: inactivation of NF1, CDKN2A, and PRC2 components, SUZ12 and EED in MPNST, leading to neurofibromin and H3K27me3 expression loss; GNAQ and GNA11 mutations in CNS primary melanocytic tumours; BRAFV600E mutation in histiocytic tumours (Langerhans cell histiocytosis and Erdheim‐Chester disease) and papillary craniopharyngioma, which provides both a diagnostic marker in the appropriate pathological setting and a therapeutic target. The WHO 2016 Classification has balanced cutting‐edge knowledge on the molecular characteristics of the miscellaneous CNS tumours reviewed here with a practical approach for their daily diagnostic work‐up. Much more progress can be expected in the classification of these neoplasms in the near future.