"Coexpression" is a term that describes anomalous expression of a T cell marker by a B cell population, a useful finding in the diagnosis of small B cell lymphomas.

The most commonly coexpressed markers are CD43 and CD5
- Expression on B cells may be fainter than on infiltrating T cells
- Comparison with another T cell marker such as CD3 is useful
When present, we consider this to be diagnostic of lymphoma

	SLL/CLL	Lymphoplasmacytic Lymphoma	Mantle Cell Lymphoma	Marginal Zone Lymphoma
CD5	80%	5%	80%	0%
CD43	80%	10-30%	84%	35%

(CD43 coexpression is seen in only 2% of splenic marginal zone lymphomas)

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