CNS tumor
Mixed gliomas
Oligoastrocytoma, NOS and anaplastic oligoastrocytoma, NOS

Author: Maxwell Rollins, M.D. (see Authors page)
Editor: Carla Ellis, M.D., M.S.

Revised: 14 October 2016, last major update October 2016

Copyright: (c) 2005-2016, PathologyOutlines.com, Inc.

PubMed Search: Oligoastrocytoma [title] OR anaplastic oligoastrocytoma [title]

Cite this page: Oligoastrocytoma, NOS and anaplastic oligoastrocytoma, NOS. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/cnstumormixedoligoastrocytoma.html. Accessed December 3rd, 2016.
Definition / General
  • The 2016 WHO classification utilizes an integrated classification, that of phenotypic and genotypic parameters for CNS tumor classification. This adds a level of objectivity that has been missing from the diagnostic process in the past, especially for this entity (Acta Neuropathol 2016;131:803)
  • Both should be exceptional (rare) diagnoses due to integration of molecular testing into the current WHO classification of gliomas (IARC: WHO Classification of Tumours of the Central Nervous System, 4th Edition, 2016)
  • Oligoastrocytoma, NOS is a glioma composed of two distinct neoplastic cell types morphologically resembling cells with either oligodendroglial or astrocytic features, and in which molecular testing could not be completed or was inconclusive; WHO grade II
  • Anaplastic oligoastrocytoma, NOS is an oligoastrocytoma, NOS with focal or diffuse microscopic features of anaplasia, including increased cellularity, nuclear atypia, pleiomorphism and increased mitotic activity; WHO grade III
Essential Features
  • Oligoastrocytoma, NOS is a glioma composed of two distinct neoplastic cell types morphologically resembling cells with either oligodendroglial or astrocytic features, and in which molecular testing could not be completed or was inconclusive; WHO grade II
  • Anaplastic oligoastrocytoma, NOS is an oligoastrocytoma, NOS with focal or diffuse microscopic features of anaplasia, including increased cellularity, nuclear atypia, pleiomorphism and increased mitotic activity; WHO grade III
Terminology
  • Per the WHO 2016, an NOS designation implies that there is insufficient information to assign a more specific code (IARC: WHO Classification of Tumours of the Central Nervous System, 4th Edition, 2016)
    • In this context, NOS in most instances refers to tumors that have not been fully tested for the relevant genetic parameter(s), but in rare instances may also include tumors that have been tested but do not show the diagnostic genetic alterations
    • NOS does not define a specific entity, but designates a group of lesions that cannot be classified into a more narrowly defined groups (Acta Neuropathol 2016;131:803)
  • The 2007 WHO classification had oligoastrocytoma as a distinct entity; however, the 2016 WHO classification has redefined it as an “not otherwise specified” category; i.e. oligoastrocytoma, NOS
  • The 2007 WHO classification had anaplastic oligoastrocytoma as a distinct entity; however, the 2016 WHO classification has redefined it as an “not otherwise specified” category, i.e. anaplastic oligoastrocytoma, NOS
ICD-10 coding
  • C71.0 Malignant neoplasm of cerebrum, except lobes and ventricles (ICD10Data.com)
Sites
  • Arises preferentially in cerebral hemispheres
Diagnosis
  • The 2016 WHO discourages diagnosis of oligoastrocytoma or mixed glioma: the diagnosis of oligoastrocytoma, NOS should remain rare, and restricted to diffuse gliomas in which histology does not allow for unequivocal categorization into either the astrocytic or oligodendroglial lineage tumors and that cannot be subjected to appropriate molecular testing or in which molecular findings are inconclusive
  • Tumors with combined IDH mutation and 1p/19q codeletion are classified "IDH mutant and 1p/q19 codeleted oligodendroglioma,” irrespective of a mixed or ambiguous histology
  • Tumors with IDH mutation but without 1p/19q codeletion are classified as “IDH mutant diffuse astrocytoma,” also irrespective of a mixed or ambiguous histology
  • Rare cases of true oligoastrocytomas do exist, with phenotypic and genotypic evidence of spatially distinct oligodendroglioma and astrocytoma components in the same tumor (Acta Neuropathol 2015;129:151)
  • The WHO supports a diagnostic algorithm for diagnosing gliomas starting with immunohistochemistry for ATRX and R132H mutant IDH1, followed by testing for 1p/19q codeletion, and then followed by IDH sequencing of tumors that are negative for the R132H mutant IDH1 immunohistochemistry (IARC: WHO Classification of Tumours of the Central Nervous System, 4th Edition, 2016)
Radiology Description
  • No specific features to separate it from oligodendroglioma or diffuse astrocytomas
  • Contrast enhancement is associated with the anaplastic variant
Micro Images

Images hosted on other servers:

Oligoastrocytoma

Positive Stains
  • GFAP (glial fibrillary acidic protein) - demonstrates glial differentiation if necessary
Molecular / Cytogenetics Description
  • A landmark molecular study looked at 405 patients with gliomas, 63 of the patients had an initial diagnosis of oligoastrocytoma, but molecular testing with IDH, 1p/19q and ATRX reclassified all 63 oligoastrocytomas into a different glioma entity (Acta Neuropathol 2015;129:133)
  • Because of the integrated approach of CNS tumor classification, most tumors classified as a oligoastrocytoma per the 2007 WHO classification criteria are now classified as an oligodendroglioma or an astrocytoma, specifically either IDH mutant and 1p/19q codeleted oligodendroglial gliomas or as IDH mutant or IDH wild type astrocytic gliomas (Curr Opin Oncol 2016 Sep 6 [Epub ahead of print])