CNS tumor

Diffuse astrocytic and oligodendroglial tumors

Oligodendroglioma, NOS

Editor-in-Chief: Debra L. Zynger, M.D.
Maria Martinez-Lage, M.D.

Topic Completed: 15 June 2019

Minor changes: 25 September 2020

Copyright: 2019-2021,, Inc.

PubMed Search: Oligodendroglioma NOS

Maria Martinez-Lage, M.D.
Page views in 2020: 4,511
Page views in 2021 to date: 3,414
Table of Contents
Definition / general
Cite this page: Martinez-Lage M. Oligodendroglioma, NOS. website. Accessed October 21st, 2021.
Definition / general
  • NOS (not otherwise specified) suffix was introduced in the 2016 WHO classification for cases in which molecular information is not available or is insufficient for a more specific diagnosis (Louis: WHO Classification of Tumours of the Central Nervous System, 4th Edition, 2016)
  • In the case of oligodendroglioma, since the entity definition requires the presence of both IDH mutation and 1p / 19q codeletion, NOS can be used whenever one or both are not known, in a tumor that morphologically shows classical features of oligodendroglioma
  • A subsequent consensus paper from a group of experts named cIMPACT-NOW clarifies that this NOS designation should be used only when results are not available (i.e. they cannot or will not be performed or they were performed but results were not obtainable after a technical failure) and not when testing was performed but did not show the typical or expected alterations (Acta Neuropathol 2018;135:481)
    • For example, in a morphologically classical oligodendroglioma with IDH mutation but no 1p / 19q codeletion or a morphologically classical oligodendroglioma without IDH mutations (after sequencing of both IDH1 and IDH2), the diagnosis should be descriptive: diffuse glioma, not elsewhere classified (NEC)
    • A detailed report describing the histological and molecular findings should always be provided when using this terminology
  • Given the uncertainty of the term NOS, which presents the treating physicians with challenges in deciding adequate treatment, the recommendation is to avoid its use and to seek as much precision as possible in the diagnosis of brain tumors
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