Marginal zone B cell lymphomas of Waldeyer's ring--a report of two tonsillectomy cases resembling histomorphological features of inflammatory lesions.

We identified two cases of lymphoma of the mucosa-associated lymphoid tissue (MALT) type in 11 tonsillectomy specimens of primary B cell lymphoma of Waldeyer's ring. Both patients were Japanese females presenting with bilateral enlargement of the palatine tonsils. One had a history of chronic otitis media. In that case, the lesion was characterized by an extrafollicular growth pattern with marginal zone-like arrangement. The tumor was mainly composed of medium-sized cells with round or indented nuclei with scant cytoplasm (centrocyte-like cells). In the other patient, most tumor cells were mature plasma cells, plasmacytoid cells, proplasmacytes, and immunoblasts with scattered centrocyte-like cells. Tropism of tumor cells for the epithelium was noted in both lesions. Primary marginal zone B cell lymphoma of the MALT type arising from Waldeyer's ring has rarely been reported in the literature, causing certain diagnostic problems. Various florid reactive lymphoproliferative disorders, including chronic tonsillitis and infectious mononucleosis, should be differentiated from this type of primary Waldeyer's ring lymphoma.