Pathological Features of Lymphoid Proliferations of the Salivary Glands: Lymphoepithelial Sialadenitis versus Low-Grade B-Cell Lymphoma of the Malt Type

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Abstract
Lymphoid proliferations of the salivary glands can be either reactive or neoplastic. Reactive lesions include the lymphoepithelial sialadenitis (LESA; also known as myoepithelial sialadenitis [MESA]) of Sjögren's syndrome. Lymphomas of the salivary glands are predominantly B-cell type and include extranodal marginal zone B-cell lymphoma of the mucosa-associated lymphoid tissue (MALT) type. The spectrum of histopathologic features of LES A/MESA includes 1) “fully benign lymphoid infiltrate,” with or without an associated lymphoid follicular structure, without immunoglobulin (Ig) light chain restriction in B-cells, and without any features of aggressive behavior, and 2) “lymphoproliferative lesions,” with or without areas of Ig light chain restriction in B-cells, with the usual presence of centrocyte-like cells. A more or less pronounced lymphoepithelial aggressiveness may be present without definite evidence of malignancy. B-cell clones are detected in over 50% of cases of LES A/MESA by molecular genetic methods, but this does not correlate with morphological or clinical evidence of overt lymphoma. On the other hand, “marginal zone B-cell lymphoma of the MALT type” of the salivary glands produces a dense lymphoid infiltrate diffusely involving the gland, with obliteration of acini. The centrocyte-like cells form broad “halos” around the epithelial cell nests and broad strands between lymphoepithelial lesions, often linking together several lymphoepithelial lesions. Further, lymphoma cells express monotypic surface Ig, and in the majority of the cases, the plasma cells are also monoclonal. In conclusion, the diagnosis of LES A/MESA versus marginal zone B-cell lymphoma of the MALT type still relies on the evaluation of morphological features. It seems that molecular genetic analysis has little or no practical role in the clinical diagnosis of salivary gland lymphoma in a setting of LESA/MESA and Sjögren's syndrome.