Immunoreactivity of B-cell markers (CD79a, L26) in rare cases of extranodal cytotoxic peripheral T- (NK/T-) cell lymphomas

The monoclonal antibodies L26 (CD20) and CD79a are very useful reagents for the immunohistochemical assessment of B-cell lineage in lymphoproliferativ e disorders. Although very few CD20-positive peripheral T-cell lymphomas (P TL) have been reported, comprehensive analyses of CD79a reactivity in extra nodal PTL and NK/T-cell lymphomas have not been performed previously. This study investigated CD79a (clone JCB117) and CD20 reactivity in 94 extranoda l non-B-cell lymphomas (enteropathy-type intestinal T-cell. lymphoma [n = 5 2], nasal NK/T-cell lymphoma [n = 11], and primary cutaneous PTL [n = 31]) and in 17 cases of nodal PTL, unspecified. In four cases (enteropathy-type intestinal T-cell lymphoma [n = 3] and nasal NK/T-cell lymphoma [n = 1)], t he majority of tumor cells stained for CD79a (all CD20 negative) and one cu taneous PTL, unspecified, was CD20 positive (CD79a negative). Extensive imm unophenotyping and polymerase chain reaction-based molecular analyses revea led that all five B-cell marker-positive extranodal lymphomas had a cytotox ic phenotype and did indeed represent monoclonal peripheral T-cell prolifer ations. To minimize the risk of misinterpretation of lymphoma cell lineage, especially in cases of extranodal lymphoproliferative disease, we suggest the use of both CD79a and CD20 in combination with a panel of antibodies re active to T cells, such as beta F1 and CD5, and to T cells and NK cells, su ch as CD3, CD2, CD56, and TIA-1.