T cell lymphoma co-expressing CD20

Abstract 

Haematological malignancies are currently classified by the WHO according to lineage, with stratification of non-Hodgkin lymphomas into B cell neoplasms, and T and NK cell neoplasms. Many laboratories routinely use CD20 and CD3 immunostains to identify B and T cell lymphomas respectively, with the use of additional immunomarkers where necessary.

We report a case of an 84-year-old male with a peripheral lymphoma which stained positively with both CD3 and CD20. PCR of DNA extracted from paraffin embedded material was positive for clonal T cell receptor gene rearrangements but negative for clonal immunoglobulin gene rearrangement supporting a diagnosis of T cell lymphoma with aberrant CD20 positivity.

This case is one of only a small number of reported cases of T cell lymphoma co-expressing CD20 and illustrates a potential pitfall in diagnosis. It emphasizes the need for 1) vigilant review of immunohistochemical stains to avoid misinterpretation and 2) the use of a wide immunohistochemical panel in lymphoma diagnosis with additional molecular studies where necessary.

Keywords: CD20 co-expression, immunohistochemistry, T cell lymphoma