Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma of the Thymus

Abstract
We present a rare case of primary low-grade B-cell lymphoma of the thymus. The tumor showed the typical features of a MALT (mucosa-associated lymphoid tissue) lymphoma with epithelium-lined thymic cyst. Histologically, there were sheets of centrocyte-like (CCL) cells intermingled with small lymphocytes and plasma cells. CCL cells invaded the epithelium of the cyst and residual Hassall's corpuscles, forming characteristic lymphoepithelial lesions. Immunohistochemically, the tumor cells revealed positive immunoreaction for CD20 and monotypic cytoplasmic restriction of kappa light chain.