Characterization of the lymphoid stroma in Warthin's tumor of salivary gland by immunohistochemistry, heavy chain gene and Bcl-2 gene rearrangement.

Warthin's tumor is rarely associated with malignant lymphoma. Only 18 cases were reported in the literature so far. In most cases the latter is a low grade process, including Marginal zone/Mucosa associated lymphoid tissue (MALT) type lymphoma, follicular lymphoma, and rarely diffuse large cell lymphoma which may arise de novo or secondary to low grade lymphoma. This study was conducted to determine the prevalence of occult B cell monoclones and genetic alterations in Warthin's tumor. Fourteen cases of Warthin's tumor were stained with antibodies to CD3, CD20, kappa and lambda light chains. On six cases of randomly selected Warthin's tumor, polymerase chain reaction (PCR) of IgH gene rearrangement (IgH-GR) was performed on genomic DNA extracted from formalin-fixed paraffin embedded tissue. One case of primary salivary gland indolent B-cell lymphoma and 3 cases of sialadenitis were analyzed by the same methods for comparison. In all Warthin's tumor and sialadenitis cases most of lymphoid stroma was B cell phenotype and concentrated in germinal centers. T cells were mostly located between germinal centers. No light chain restriction was demonstrable by kappa and lambda immunostains. Molecular genetic studies failed to show IgH-GR by FISH and showed polyclonal by IgH PCR. In contrast, the lymphoma case showed a diffuse proliferation of small B cells with light chain restriction and a minor component of reactive T cells. FISH showed IgH-GR and bcl-2 gene translocation with monoclonality by IgH PCR. Our study concludes that the lymphoid stroma of Warthin's tumor is reactive.