[1210] B-Cell Neoplasms with Aberrant T-Cell Antigen Expression Show Plasmacytic Differentiation

JL Herrick, KL Grogg, WR Macon, A Dogan, AL Feldman. Mayo Clinic College of Medicine, Rochester, MN

Background: Phenotyping for B- and T-cell lineage-associated antigens is an integral part of lymphoma diagnosis and classification. While CD20-positive T-cell lymphomas are well-documented, B-cell neoplasms (BCN) expressing CD3 or other T-cell antigens (TCAs) (excluding CD5 and CD43) have been reported only rarely. Such cases can represent a diagnostic pitfall, since unifying pathologic features of such cases have not been identified. We compiled a series of BCNs with aberrant TCA expression and assessed morphologic and immunophenotypic features to provide a clearer understanding of these rare neoplasms.
Design: BCNs evaluated at the Mayo Clinic were reviewed for aberrant TCA expression on initial immunohistochemical panels. All identified cases were evaluated for CD2, CD3, CD4, CD5, CD7, CD8, CD19, CD20, CD22, CD30, CD56, CD79a, PAX-5, TIA-1, BetaF1, and MUM1/IRF4 by immunohistochemistry. EBV encoded RNA was assessed using in situ hybridization. PCR studies for T-cell receptor and immunoglobulin gene rearrangements were performed in 7 cases.
Results: 14 BCNs expressed TCAs including 10 diffuse large B-cell lymphomas (DLBCL) (3 nodal, 7 extranodal), 3 plasmacytomas (all extranodal), and one nodal follicular lymphoma, grade 3A (FL). 9/14 cases showed some degree of plasmacytic differentiation (6/11 lymphomas and 3 plasmacytomas). 8/14 (57%) were positive for CD20. 12/14 (86%) showed CD3 expression, 4/13 (31%) expressed CD4 and 3/13 (23)% expressed CD8. Most cases expressed only one TCA, predominantly CD3. One case expressed two TCAs. Three cases expressed multiple TCAs (2 DLBCL and 1 FL). All cases were positive for MUM1/IRF4. 2 cases were EBV positive (DLBCLs). All tested cases showed clonal immunoglobulin gene rearrangements with no clonal T-cell receptor gene rearrangement detected.
Conclusions: Most BCNs with aberrant TCA expression show plasmacytic differentiation and express the transcription factor MUM1/IRF4. Since lymphomas with plasmacytic differentiation often lack CD20, T-antigen expression may falsely lead to an impression of T-cell lymphoma. To avoid this pitfall, lineage should be assessed with a panel of B- and T-cell antigens and molecular studies performed in ambiguous cases. Aberrant antigen expression might result from disrupted B-cell transcriptional programming, a hypothesis that merits further study. For example, B-cell programming is disrupted in classical Hodgkin lymphomas and primary effusion lymphomas both of which express MUM1/IRF4 and may aberrantly express TCAs.
Category: Hematopathology

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 182, Wednesday Morning