Systemic CD5+ MALT lymphoma: presentation with Waldenstrom syndrome.

We report a case of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) in a 75-year-old woman with a neuropathy related to high levels of serum immunoglobulin M and a history of rheumatoid arthritis and polymyositis. The patient developed a mass in the right submandibular salivary gland, and this mass demonstrated histopathologic features that are typical of MALT lymphoma, including infiltrates of small monocytoid B cells in the epithelium (forming "lymphoepithelial lesions"), a reactive background of florid germinal center hyperplasia, and follicular colonization by the monocytoid B cells. Many plasma cells in the background expressed cytoplasmic immunoglobulin M lambda, matching the serum spike. Flow cytometric analysis confirmed the presence of clonal mature B cells; however, unlike most MALT lymphomas, these cells coexpressed dim CD5. Clinical staging revealed evidence of systemic distribution with documented disease involving the bone marrow, the lung, and a paratracheal lymph node. Analysis of this unusual systemic MALT lymphoma, and a comparison with similar examples from the literature, illuminates relationships among MALT lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, and Waldenstrom macroglobulinemia.