Peripheral T-cell lymphoma with aberrant expression of CD79a and CD20: A diagnostic pitfall

Immunohistochemical studies are increasingly used for the routine diagnosis of lymphomas as it is widely accepted that lymphomas of different cell lin eages vary in their prognosis and response to therapy. A case of peripheral T-cell lymphoma with aberrant expression of B-cell-associated antigens L-2 6 (CD20) and mb-1 (CD 79a) is described. The disease pursued al aggressive clinical course, and the patient died of disease 6 weeks after presentation . Immunohistochemical studies demonstrated expression of both T- and B-cell-a ssociated antigens, including CD3, CD8, CD43, TIA-1, CD20, and CD79a. Other markers expressed by the tumor cells included CD56 and S-100. Of interest, betaF-1 staining for the beta chain of T-cell receptor (TCR) complex was p ositive in the small admired T lymphocytes but was negative in the tumor ce lls, raising the possibility of a gamma/delta T-cell lymphoma Molecular stu dies by polymerase chain reaction (PCR) demonstrated clonal TCR-gamma chain gene rearrangement without evidence for a clonal rearrangement of the immu noglobulin heavy chain gene. PCR for HHV-8 related sequences was negative. Mh-1 is an IgM-associated protein that was thought to be restricted to norm al and neoplastic B cells. Although its coexpression has been reported in u p to 10% cases of precursor T-cell lymphoblastic lymphoma the coexpression of both CD20 and CD79a has not been described in mature T-cell malignancies . Biphenotypic lymphomas associated with HHV-8 have been reported in immuno deficiency, but no evidence of immune deficiency was identified, and studie s for EBV and HHV-8 were negative. This case illustrates that no marker has absolute lineage specificity and that immunophenotypic studies should alwa ys be performed with panels of monoclonal antibodies. Moreover, cases with ambiguous phenotypes may require genotypic studies for precise lineage assi gnment.