• Very rare in thymus, < 20 cases reported

• May arise without underlying autoimmunity (Lung 2011;189:461); these cases often involve males or older patients (Leuk Lymphoma 2011;52:2276)

• 36 year old woman with Sjögren syndrome and coexisting thymic and gastric MALT (Arch Pathol Lab Med 2000;124:770)
• 63 year old woman with possible connective tissue disease (Hum Pathol 2000;31:255)
• Patient with Sjögren syndrome and cryoglobulinemia (Pathology 2009;41:701)

• Centered in thymus

• Clusters of centrocyte-like lymphoid cells in lymphoepithelial lesions mixed with mature lymphocytes and lymphoid follicles with reactive germinal centers
• Also plasma cells
• Variable microcysts
• Early MALT cases in patients with thymic lymphofollicular hyperplasia and myasthenia gravis or connective tissue disease have ill-defined lymphoid follicles with sheets of centrocyte-like B cells disrupting the medullary epithelial cytokeratin network

Thymic tumor

• CD20, CD45, CD79a, monotypic immunoglobulin light chain; variable bcl2 and CD10

• CD5, CD10, CD23, CD43, CD99, bcl6, TdT

• Nuclei with irregular protrusions or blebs
• No intercellular junctions, no cytoplasmic filament bundles, neurosecretory granules, synaptic vesicles, microtubules, basal lamina, cytoplasmic processes or primitive sarcomeres

• Trisomy 3 may play a role in lymphoma development (Pathol Int 2012;62:93)
• Thymic MALT lymphomas have a characteristic pattern of chromosomal aberrations that may be similar to those of other autoimmune-associated MALT lymphomas
• Monoclonal IgH rearrangement present (Am J Clin Pathol 2002;117:51)

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