Stains & CD markers
PAX5


Last author update: 10 May 2022
Last staff update: 10 May 2022

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PubMed Search: PAX5

Austin Ellis, M.D.
Ling Zhang, M.D.
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Cite this page: Ellis A, Zhang L. PAX5. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/stainspax5.html. Accessed August 17th, 2022.
Definition / general
Essential features
  • Nuclear marker expressed in most mature and immature B cell neoplasms
  • Especially useful when the B cell neoplasm does not express CD20 (such as in classic Hodgkin lymphoma, B lymphoblastic leukemia / lymphoma or status post rituximab therapy)
  • Not expressed in plasma cells due to repression by BLIMP1
  • Variable expression in Merkel cell carcinoma, small cell carcinoma, rectal neuroendocrine tumors and acute myeloid leukemia with t(8;21)(q22;q22)
Terminology
  • Also known as B cell lineage specific activator protein (BSAP)
Pathophysiology
  • Encoded by PAX5 at 9q13
  • Paired box transcription factors have a novel, highly conserved DNA binding motif and regulate early tissue development
  • Activates B cell specific genes and represses genes specific for other hematopoietic lineages (Oncogene 2012;31:966)
  • Regulates distinct target genes in early and late B cell development (EMBO J 2012;31:3130)
  • Activates expression of factors required for the BCR signaling pathway (Med Oncol 2015;32:360)
  • Critical regulator of human primordial germ cell development (Nat Cell Biol 2018;20:655)
Interpretation
  • Nuclear stain
Uses by pathologists
  • Identification of mature and immature B cell neoplasms
  • Determining B cell lineage in lymphomas that lack CD20 expression
  • Reference: Adv Anat Pathol 2007;14:323
Prognostic factors
Microscopic (histologic) images

Contributed by Austin Ellis, M.D. and Ling Zhang, M.D.

Classic Hodgkin lymphoma

Classic Hodgkin lymphoma (PAX5)

Diffuse large B cell lymphoma

Diffuse large B cell lymphoma (CD3)

Diffuse large B cell lymphoma (CD20)

Diffuse large B cell lymphoma (PAX5)


Follicular lymphoma

Follicular lymphoma (CD3)

Follicular lymphoma (CD20)

Follicular lymphoma (PAX5)

Follicular lymphoma (CD10)

Follicular lymphoma (BCL6)


Follicular lymphoma (BCL2)

Follicular lymphoma (CD21)

Merkel cell carcinoma

Merkel cell carcinoma (CD45)

Merkel cell carcinoma (synaptophysin)

Merkel cell carcinoma (PAX5)

Virtual slides

Images hosted on other servers:
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Classic Hodgkin lymphoma

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Follicular lymphoma

Positive staining - normal
Positive staining - disease
Negative staining
Sample pathology report
  • Lymph node, needle core biopsy:
    • Diffuse large B cell lymphoma, germinal center B cell type (see comment)
    • Comment: The needle core biopsy demonstrates sheets of large atypical lymphoid cells. The neoplastic cells are positive for CD20, PAX5, CD10, BCL6 and BCL2 and negative for CD3, CD5, MUM1 and MYC. Ki67 is variable, on average 70%. CD21 is negative. FISH for high grade B cell lymphoma is pending and will be reported in an addendum.
Board review style question #1

A 27 year old man presents with fever, drenching night sweats and supraclavicular lymphadenopathy. Excisional biopsy of the enlarged lymph node has architectural effacement by variable numbers of large cells with prominent nucleoli, mixed with inflammatory cells. The large cells are positive for CD30 and PAX5 and negative for CD3 and CD20. Which of the following is true regarding the large cells?

  1. PAX5 expression indicates that they are derived from B cells
  2. PAX5 expression indicates that they are plasma cells
  3. PAX5 expression supports a diagnosis of anaplastic large cell lymphoma
  4. PAX5 expression supports a diagnosis of seminoma
Board review style answer #1
A. PAX5 expression indicates that they are derived from B cells

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Reference: PAX5
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