A comparative analysis of cutaneous marginal zone lymphoma and cutaneous chronic lymphocytic leukemia.

The morphologic distinction between cutaneous marginal zone lymphoma (CMZL) and secondary cutaneous involvement by B-cell chronic lymphocytic leukemia (B-CLL) can be difficult. Both entities can show very similar architectural patterns of involvement in the skin and not uncommonly, the skin can be the first site of presentation of B-CLL in the elderly. We reviewed biopsies of 13 patients with cutaneous B-CLL and 14 patients with CMZL to compare their histologic and immunohistochemical features. CMZL and cutaneous B-CLL both predominantly exhibited a nodular pattern of skin involvement (9 of 13 B-CLL, 9 of 14 CMZL) with a minority of cases demonstrating a diffuse pattern (4 of 13 B-CLL, 4 of 14 CMZL). Although reactive germinal centers (12 of 14 cases) and plasma cells (10 of 14 cases) were seen more often in CMZL, plasma cells were also observed in cases of B-CLL (4 of 13). The lesional cells of B-CLL expressed CD79, CD5, CD23, and CD43, although CMZL did not express CD5 or CD43. Although we noted light chain restriction in 13 of 14 cases of CMZL cases, we also observed light chain restriction in 4 of 13 cases of B-CLL. Our results indicate that CMZL and B-CLL can be morphologically similar and both may show light chain restriction. Complete immunophenotyping is necessary to ensure that all cases are correctly classified.