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Extranodal Marginal Zone Lymphoma of Mucosa-Associated Lymphoid Tissue Involving the Parotid Gland

Extranodal marginal zone lymphomas of mucosa-associated lymphoid tissue (MALT lymphomas) are small B-cell lymphomas that arise from acquired MALT in sites of chronic inflammation associated with infection or autoimmune disease. Mucosa-associated lymphoid tissue lymphoma arising in the parotid gland is an indolent disease with a low rate of dissemination. Histologic features of parotid gland MALT lymphoma include a diffuse lymphocytic infiltration with distortion of the normal lobular gland architecture and lymphocytic infiltration of the interlobular connective tissues and periglandular soft tissues. Lymphoepithelial lesions with intraepithelial B cells causing distortion/destruction of the ductular epithelium are typically present. The neoplastic B cells consist mainly of small B cells, including centrocyte-like cells and monocytoid B cells, which are present throughout the lymphocytic infiltrate, including areas distant from residual reactive follicles. In many cases, the centrocyte-like or monocytoid B cells are present as sheet-like proliferations with frequent accentuation around the lymphoepithelial lesions. Accumulations of plasma cells may show light-chain restriction. Herein, we present a case of parotid gland MALT lymphoma and summarize current knowledge regarding histologic and immunophenotypic features, cytogenetic and molecular associations, outcome data, and differential diagnostic considerations.