Histopathology

Most NHL of the oral cavity and oropharynx are of B-cell lineage, with DLBCL being the commonest (>50%) {370,1476, 1704,2142,2530}. The surface stratified squamous epithelium is either intact or ulcerated. The stroma is densely infiltrated by lymphoma cells, which vary in appearance depending on the histologic type. In the tonsil, not uncommonly there are some residual lymphoid follicles due to incomplete involvement of the tissue.

Diffuse large B-cell lymphoma (DLBCL) DLBCL is characterized by large to medium-sized cells which may resemble cen-troblasts. Nuclear multilobation is prominent in some cases. There can be areas of coagulative necrosis. In DLBCL of the tonsils, a focal follicular pattern may be present {2138}, and it has been argued that the follicles result from colonization of pre-existing follicles rather than de novo neoplastic follicle formation. In some cases, there may be an associated component of extranodal marginal zone B-cell lymphoma of MALT type or follicular lymphoma, indicating that the DLBCL represents high-grade transformation of the latter {1998}.

Mantle cell lymphoma

Lymphoma cells are usually monotonous, and frequently have small irregular nuclei, dense chromatin and scanty cytoplasm. They may show a mantle zone distribution around residual follicles. Rare cases can have a blastic appearance and are associated with a higher proliferation rate {19}.

Follicular lymphoma

Follicular lymphoma is characterized by follicles that frequently lack polarity and mantle zone. The neoplastic follicles consist of a mixture of centrocytes and cen-troblasts, often without accompanying tingible-body macrophages.

Extranodal marginal zone B-cell lymphomas of MALT type

These lymphomas most often involve the tonsil, and less commonly the palate, gingiva, buccal mucosa, tongue and lip {295,962,1476,1507,1629,1998,2225, 2531}. The surface epithelium is often intact. In a background of reactive lym-phoid follicles, there is an interfollicular and perifollicular infiltrate of small to medium-sized cells with roundish or indented nuclei. Some cells have a moderate amount of clear cytoplasm, resembling monocytoid B-cells. There can be clusters of admixed plasma cells. Follicular colonization can be seen in some cases. A distinctive feature is invasion of the epithelial component (e.g. sur-

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