CNS tumor

Diffuse astrocytic and oligodendroglial tumors

Anaplastic astrocytoma, NOS

Editor-in-Chief: Debra L. Zynger, M.D.
John DeWitt, M.D., Ph.D.

Topic Completed: 14 January 2020

Minor changes: 7 May 2021

Copyright: 2002-2021,, Inc.

PubMed Search: Anaplastic astrocytoma[TI] central nervous system

John DeWitt, M.D., Ph.D.
Page views in 2020: 4,178
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Cite this page: DeWitt J. Anaplastic astrocytoma, NOS. website. Accessed October 23rd, 2021.
Definition / general
Essential features
  • The 2016 WHO defines a not otherwise specified (NOS) designation appropriate when diagnostic information (histological or molecular) necessary to assign a more specific WHO designation is not available
  • Based on 2016 WHO recommendations, full assessment of IDH mutational status includes sequence analysis of IDH1 codon 132 and IDH2 codon 172 when R132H-IDH1 immunohistochemistry is negative
  • Therefore, a histologic anaplastic astrocytoma with a negative R132H-IDH1 stain would be assigned a diagnosis of anaplastic astrocytoma, NOS in the absence of molecular testing for definitive IDH status
  • See Anaplastic astrocytoma, IDH-mutant and Anaplastic astrocytoma, IDH-wildtype for further features, imaging, microscopic, etc
ICD coding
  • ICD-10: C71.9 - malignant neoplasm of brain, unspecified
  • Grade III of IV
Board review style question #1
    You are working up a diffusely infiltrating astrocytic glial tumor that shows mitotic activity and pleomorphism but no evidence of necrosis or microvascular proliferation. Immunohistochemical work up reveals tumor cells are negative for R132H-IDH1 and retain ATRX. What is the proper diagnosis given the available information?

  1. Anaplastic astrocytoma, IDH-wildtype
  2. Diffuse astrocytoma, IDH-wildtype
  3. Glioblastoma, IDH-wildtype
  4. Anaplastic astrocytoma, NOS
  5. Diffuse astrocytoma, NOS
Board review style answer #1
D. Anaplastic astrocytoma, NOS

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