CD20 positive T-cell lymphoma/leukemia: a rare entity with potential diagnostic pitfalls.

Mature T-cell neoplasms are relatively uncommon, accounting for approximately 10% of all non-Hodgkin lymphomas. This category of hematopoietic neoplasms is clinically aggressive and shows a poor response to therapy and shortened survival. The antigen CD20 has long been thought to be a specific marker for B-cell lineage and has been used to help differentiate T-cell and B-cell neoplasms. We present two cases of a rare subset of T-cell leukemia/lymphoma having a unique immunophenotype, both being CD20+. The significance of CD20 antigen in T-cell lymphomas is yet to be determined, but may allow treatment with novel therapeutic agents (eg, rituximab, a recombinant anti-CD20 monoclonal antibody).