MALT Lymphomas: Epidemiology and Infectious Agents

In 1983 Isaacson and Wright observed that low grade lymphomas arising from the stomach, thyroid, salivary glands and lung exhibit histological features that reproduce the architecture of mucosa associated lymphoid tissue (MALT) rather than that of similar lymph node tumor. The tumor cells are located in the marginal zone surrounding the mantle, and like the B cells of the marginal zone of Peyer\'s patches and tonsils, invade the overlying epithelium, forming the so-called “lymphoepithelial lesion“; like normal MALT, these lymphomas have reactive lymphoid follicles. MALT lymphomas have been defined as extranodal marginal zone B-cell lymphomas of MALT type both in the REAL classification and in the last WHO Classification. These tumors present an indolent natural course, since they tend to remain localized for long periods and show a good response to the therapy. They usually arise from organs where MALT is physiologically absent and is acquired following a persistent antigenic stimulation by an infectious agent or by an autoimmune process.