Stains & CD markers

Editorial Board Member: Elizabeth Courville, M.D.
Deputy Editor-in-Chief: Genevieve M. Crane, M.D., Ph.D.
Leonie Frauenfeld, M.D.
Christian M. Schürch, M.D., Ph.D.

Last author update: 18 January 2022
Last staff update: 19 September 2022

Copyright: 2003-2024,, Inc.

PubMed Search: CD20

Leonie Frauenfeld, M.D.
Christian M. Schürch, M.D., Ph.D.
Page views in 2023: 15,143
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Cite this page: Frauenfeld L, Schürch CM. CD20. website. Accessed May 19th, 2024.
Definition / general
  • Common B cell marker (also CD19, CD79a, PAX5)
  • Also called L26, membrane spanning 4 domains (MS4A1)
Essential features
  • Widely used B cell marker (also CD19, CD79a, PAX5)
  • Retained on mature B cells until plasma cell differentiation
  • Anti-CD20 therapy (e.g., rituximab) is available for treatment of non-Hodgkin B cell lymphoma and autoimmune diseases
  • 33kd phosphoprotein with 3 hydrophobic regions that traverse the cell membrane, creating a structure similar to an ion channel that allows for the influx of calcium required for cell activation
  • Initially expressed on B cells after CD19 / CD10 expression and before CD21 / CD22 and surface immunoglobulin expression; retained on mature B cells until plasma cell differentiation
  • Delivers early signal in B cell activation
  • FMC7 detects a conformational epitope on the CD20 molecule with probable cholesterol dependency (Cytometry 2001;46:98, Leukemia 2003;17:1384)
Clinical features
Uses by pathologists
  • Commonly used B cell marker used in the workup of benign and malignant processes
Case reports
  • 21 year old man with nodular lymphocyte predominant Hodgkin lymphoma with large atypical cells (Case #284)
Microscopic (histologic) images

Contributed by Leonie Frauenfeld, M.D., Andrey Bychkov, M.D., Ph.D. and Kaveh Naemi, D.O.
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Germinal center with strong CD20 positive B cells

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SLL / CLL infiltrate in a lymph node

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Hairy cell leukemia infiltrate in the bone marrow

MALT lymphoma

Burkitt lymphoma
of ileocecal valve

Cases #101, 118, 127, 130, 284 and AFIP images

Lymph node: angiomyomatous hamartoma

Skin: halo nevus

MALT lymphoma of stomach

Myeloid sarcoma of bone (negative)

NK / T cell lymphoma, nasal type (tumor cells are negative)

T cell lymphoma

Hodgkin lymphoma, nodular lymphocyte predominant subtype

Positive staining - normal
  • Most B cells (considered a pan-B cell antigen), also follicular dendritic cells
  • Hematogones can be CD20+ (acquire CD20 during maturation) and a panel is useful in distinguishing them from leukemia cells (Am J Clin Pathol 2000;114:66, Blood 2001;98:2498)
Positive staining - disease
Negative staining
  • Nonhematopoietic cells, most T cells, basophils, plasma cells and mast cells
  • Note: staining does not work well with Bouin fixative
Flow cytometry description
  • CD20 can be evaluated by flow cytometric immunophenotyping as well as immunohistochemical stains
  • Dim or bright CD20 expression can provide clues to diagnoses
    • Brighter expression in follicular lymphomas than normal B cells (Am J Clin Pathol 2005;124:576)
    • In chronic lymphocytic leukemia / small lymphocytic lymphoma (CLL / SLL), CD20 expression may be dim to negative
Sample pathology report
  • Lymph node, excision:
    • Diffuse large B cell lymphoma (DLBCL)
    • Comment: Lymph node presents with effaced architecture and demonstrates a dense, sheet-like proliferation of immunoblastic cells with strong, homogeneous CD20 positivity. Additionally, the cells mark positive for CD10 and BCL6 but are negative for MUM1, according to a germinal center type DLBCL (Hans algorithm). The cells are positive for BCL2 and weakly positive for MYC (20%).
Board review style question #1

Which normal cell type is most associated with CD20 expression?

  1. Basophils
  2. Germinal center B cell
  3. Plasma cells
  4. T cells
Board review style answer #1
B. Germinal center B cell

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Reference: CD20
Board review style question #2
CD20 is the target of monoclonal antibodies used in the therapy against

  1. Anaplastic large cell lymphoma
  2. Mycosis fungoides
  3. Rheumatoid arthritis
  4. T cell large granular lymphocytic leukemia (T-LGL)
Board review style answer #2
C. Rheumatoid arthritis

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Reference: CD20
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