# CD20 expression (CD20-positive)

Source: https://onco.cc/biomarkers/cd20-expression/  
OnCo record `cd20-expression` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

CD20 is the B-cell antigen rituximab made famous. Rituximab and obinutuzumab labels are written for CD20-positive lymphoma and leukaemia; the newer CD20 x CD3 bispecifics assume it.

## Summary

CD20 is read by immunohistochemistry or flow cytometry and is present on almost all mature B-cell lymphomas and chronic lymphocytic leukaemia. Rituximab (Rituxan) is labelled as a CD20-directed cytolytic antibody for CD20-positive non-Hodgkin lymphoma and CLL; obinutuzumab (Gazyva) for CLL and follicular lymphoma; mosunetuzumab, glofitamab and epcoritamab are CD20 x CD3 bispecifics labelled by histology. CD20-negative lymphomas (some after rituximab, and entities such as plasmablastic lymphoma) are excluded from the anti-CD20 indications.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: CD20-positive; CD20+; CD20 expression; CD20 positive lymphoma; CD20 loss
- Tags: biomarker; surface-antigen

## Notes

- Lymphoma: the stain is part of every diagnostic panel and is not repeated before each dose of rituximab, which is why loss at relapse is under-measured. Of 124 patients treated with rituximab-containing chemotherapy, 36 relapsed or progressed, 19 were rebiopsied and 5 of those, 26.3%, had become CD20-negative, with lower CD20 messenger RNA in the negative cells than in the positive cells from the same patient; all five died within a year (Hiraga 2009). The practical rule is to rebiopsy and restain before giving another CD20-directed drug. CD20 is not internalised, so it carries naked antibodies and T-cell engagers but no antibody-drug conjugate.

## Sources

- Rituxan prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b172773b-3905-4a1c-ad95-bab4b6126563
- Hiraga et al., Blood 2009: CD20-negative transformation after rituximab-containing chemotherapy (19 rebiopsied patients): https://doi.org/10.1182/blood-2008-08-175208

## Connected records

- biomarkers: [CD19 expression (CD19-positive)](https://onco.cc/biomarkers/cd19-expression/), [CD22 expression (CD22-positive)](https://onco.cc/biomarkers/cd22-expression/)
- cancers: [Chronic lymphocytic leukaemia](https://onco.cc/cancers/cll/), [Diffuse large B-cell lymphoma](https://onco.cc/cancers/dlbcl/), [Follicular lymphoma](https://onco.cc/cancers/follicular-lymphoma/), [Mantle cell lymphoma](https://onco.cc/cancers/mantle-cell-lymphoma/), [Marginal zone lymphoma](https://onco.cc/cancers/marginal-zone-lymphoma/), [Non-Hodgkin lymphoma (all types)](https://onco.cc/cancers/non-hodgkin-lymphoma/)
- drugs: [Epcoritamab](https://onco.cc/drugs/epcoritamab/), [Glofitamab](https://onco.cc/drugs/glofitamab/), [Mosunetuzumab](https://onco.cc/drugs/mosunetuzumab/), [Obinutuzumab](https://onco.cc/drugs/obinutuzumab/), [Rituximab](https://onco.cc/drugs/rituximab/)
- terms: [Antigen escape (antigen loss, lineage switch)](https://onco.cc/terms/antigen-escape/), [Antigen escape: how a lymphoma loses the thing the drug was aimed at](https://onco.cc/terms/lymphoma-bio-antigen-escape/), [Flow cytometry (immunophenotyping)](https://onco.cc/terms/flow-cytometry/), [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [What it costs to aim at a lineage antigen](https://onco.cc/terms/lymphoma-bio-lineage-antigen-cost/)
- targets: [CD20](https://onco.cc/targets/cd20/)

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