T-cell-rich B-cell lymphoma presenting in skin. A clinicopathologic analysis of six cases.

We reviewed our experience with six T-cell-rich B-cell lymphomas (TRBL) presenting in skin. Immunohistochemical studies were performed on all biopsies. The lymphoid population consisted mainly of CD3 and/or UCHL-1 (CD45RO) positive T cells. 5 to 15% of the lymphoid cells stained for the B-cell marker L26 (CD20). Monoclonality of the B-cell component was demonstrated in all cases, utilizing either light chain restriction (5 cases) or clonal immunoglobulin heavy chain gene rearrangement by polymerase chain reaction (PCR) (2 cases). One case was confirmed to be monoclonal by both techniques. Additionally, no clonal rearrangements of the T-cell receptor gamma gene were observed. There was considerable morphological variety in these cases. In H&E stained sections, the differential diagnosis included pseudolymphoma, peripheral T-cell lymphoma, Hodgkin's disease, Lennert's lymphoma and a MALT lymphoma. A significant component of monoclonal plasma cells was present in 3 of 6 cases, suggesting a possible origin from cutaneous immunocytoma. In fact, one of our cases was a biphasic lymphoma displaying TRBL with a small focus of immunocytoma. We conclude that immunophenotypic analysis is necessary for the diagnosis of TRBL. Pathologists should be aware of this type of cutaneous B-cell lymphoma to avoid misinterpretation as a pseudolymphoma.