CD Markers

Topic Completed: 1 February 2002

Minor changes: 4 January 2021

Copyright: 2002-2021,, Inc.

PubMed Search: CD99 [title]

Nat Pernick, M.D.
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Cite this page: Pernick N. CD99. website. Accessed January 22nd, 2021.
Definition / general
  • Also called MIC2, O13, T cell surface glycoprotein E2
  • Encoded by pseudoautosomal gene on short arms of X and Y
  • Part of Xg blood group system (NCBI)
  • Functions: cell surface glycoprotein involved with
    1. Differentiation of primitive neuroectodermal cells (Exp Mol Med 2003;35:438)
    2. Apoptosis of T cells (FEBS Lett 2003;554:478)
    3. T cell adhesion
    4. Migration of leukocytes
    5. In Ewing / PNET, may promote growth and migration of tumor cells via downregulation of KCMF1 (potassium channel modulatory factor), a possible metastasis suppressor gene (Oncogene 2006;25:2795)
  • Associated with EWS-FLI1 fusion transcript, t(11;22)(q24;q12), causing FLI-1 protein overexpression
  • Distinct membranous staining for Ewing / PNET; cytoplasmic for other tumors
Uses by pathologists
  • Relatively nonspecific marker for Ewing sarcoma and T cell lymphoma, but does distinguish Ewing from neuroblastoma (Hum Pathol 1993;24:880)
  • Also distinguishes meningeal hemangiopericytoma (CD99+) from anaplastic meningiomas (CD99 weak / focal / negative, Hum Pathol 2004;35:1413)
  • Detect minimal residual disease by CD99+ flow cytometry in TALL (Leukemia 2004;18:703)
  • Anti-CD99 antibody may have therapeutic value (Eur J Cancer 2006;42:91)
Microscopic (histologic) images

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Histologic and
features of Ewing's

Positive staining - normal
Positive staining - disease
Negative staining
Additional references
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