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Primary thymic marginal zone B-cell lymphoma (MZBL) of mucosa-associated lymphoid tissue (MALT)-type is a very rare disease with distinct clinicopathologic features. I herein report a rare case of primary thymic MZBL of MALT-type arising in the thymus in a patient with Sjogren´s syndrome and rheumatoid arthritis. A mediastinal mass was detected by computerized tomography in a 43-yr-old Korean woman with a history of Sjogren´s syndrome and rheumatoid arthritis and the thymus was resected through median sternotomy. The solid and nodular tumor (7x6x3cm) was confined in the thymus. Histologically, the lymphoid infiltrate comprised monotonous centrocyte-like cells with monocytoid cells, small lymphocytes, and plasma cells. Prominent lymphoepithelial lesions were formed by centrocyte-like cells infiltrating the Hassall´s corpuscles. Immunohistochemically, the tumor cells were positive for CD20, CD79a, and bcl-2 and negative for CD3, CD5, CD10, CD23, and bcl-6. IgA and kappa light chain restriction were also found in plasma cells in the tumor. Sjogren´s syndrome and rheumatoid arthritis are known to be associated with MALT lymphoma and were considered to play an important role in the development of malignant lymphoma in this patient.
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