Lymphoma of the thyroid gland.

Abstract

Lymphoma of the thyroid is uncommon but its exact incidence is unknown. Thyroid lymphoma almost always arises against a background of Hashimoto’s thyroiditis, the relative risk of a patient with Hashimoto’s thyroiditis developing lymphoma being 67 (Holm et al. 1985). In 1984 Isaacson and Wright noted close histological and clinical similarities between low-grade B-cell lymphomas of the stomach, salivary gland, lung and thyroid. The histological features of these lymphomas appeared to recapitulate those of mucosa-associated lymphoid tissue (MALT), as typified by Peyer’s patches, and the term “MALT lymphoma” was coined to describe this group of extranodal lymphomas (Isaacson and Wright 1984). Unlike the other common sites where MALT lymphomas occur, the thyroid cannot be described as a mucosal organ. As the MALT concept has developed, however, it has become clear that the common theme is not necessarily that the lymphomas arise in mucosae but, rather, that they arise from acquired lymphoid tissue with features of MALT; these include lymphoid follicles and adjacent epithelium containing intraepithelial B-cells, the so-called lymphoepithelium. Functionally, MALT differs from nodal lymphoid tissue in that antigens gain access directly across the lymphoepithelium rather than via afferent lymphatics.