CD5-positive mucosa-associated lymphoid tissue (MALT) lymphoma: a clinicopathologic study of 14 cases

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) is a B-cell neoplasm that is typically CD5 negative. We describe the clinicopathologic, immunophenotypic, and cytogenetic features of 14 cases of CD5+ MALT lymphoma. There were 9 men and 5 women (median age, 68 years; range, 34-87 years). MALT lymphoma was initially diagnosed in salivary glands (n = 4), nasopharynx (n = 2), and 1 case each in conjunctiva, thyroid, stomach, colon, skin, lung, kidney, and retroperitoneum. Two patients had localized disease; 9 had disseminated disease with generalized lymphadenopathy (n = 8), multifocal lymphoma (n = 6), or bone marrow involvement (n = 5). No staging information was available for the remaining patients. None presented with B symptoms, splenomegaly, cytopenias, lymphocytosis, monoclonal gammopathy, or elevated serum lactate dehyrogenase. Serum β2-microglobulin was elevated in 6. Morphologically, the neoplasms had features typical of MALT lymphoma being composed of small- to medium-sized cells with round to slightly irregular nuclear contours and moderate amount of cytoplasm. Lymphoepithelial lesions were noted in 4 cases. CD5 was positive in all cases by immunohistochemistry (n = 12) and/or flow cytometry (n = 11). All cases assessed were negative for cyclin D1 (13/13) and CD10 (11/11). Conventional cytogenetics in 7 cases showed trisomy 3 in 3 and diploid in 4. With a median follow-up of 71 months (range, 2-131 months), overall survival at 5 years was 100%, although 5 patients required chemotherapy. Our results show that CD5 expression is rare in MALT lymphoma, and is often associated with nongastric disease and an increased tendency to present with disseminated disease. Overall survival is excellent with appropriate therapy.