Author: Nat Pernick, M.D. (see Authors page)

Revised: 2 December 2015, last major update January 2013

Copyright: (c) 2002-2015,, Inc.

PubMed Search: PAX5 [title]

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Cite this page: PAX5. website. Accessed January 18th, 2019.
Definition / general
  • Also called BSAP, a B cell-lineage specific activator protein at 9q13
  • Member of paired box (PAX) family of transcription factors, which have a novel, highly conserved DNA-binding motif, known as the paired box
    • Encodes BSAP expressed at early stages of B-cell differentiation, also in developing CNS and testis (Wikipedia - PAX5)
  • Detected in B cells from pro-B cell stage to plasma cell stage where it is downregulated (Clin Med Res 2010;8:84)
  • Required for progression of B cell development beyond the early pro-B cell stage (Cancer Res 2011;71:7345)
Uses by pathologists
  • Detection of pre-B cells (PAX5+, more sensitive and specific than CD20)
  • Diagnosis of Reed-Sternberg cells in classic Hodgkin lymphoma (PAX5+) versus T / null cell anaplastic large cell lymphoma (PAX5-, although rarely positive in T cell lymphomas, Mod Pathol 2010;23:593)
  • Diagnosis of lymphoplasmacytic lymphoma / plasmacytoid differentiation in marginal zone lymphoma (PAX5+) versus plasmacytoma (PAX5-, Am J Surg Pathol 2002;26:1343)
Microscopic (histologic) images

Images hosted on Other servers:

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Classical Hodgkin lymphoma

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Rare PAX5+ anaplastic large cell lymphoma

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Uterus (endometrium), mesonephric adenocarcinoma

Positive staining - normal
  • B cells from pro-B cell stage to plasma cell stage, where it is down regulated
Positive staining - disease
Negative staining
  • Carcinoid tumor, embryonal carcinoma, myeloma, plasmacytoma, seminoma, T cell lymphoma
Molecular / cytogenetics images
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Anaplastic large cell lymphomas