Extranodal oral lymphomas: Histologic subtypes and immunophenotypes (in routinely processed tissue)

Twenty-seven extranodal oral lymphomas were subclassified according to the National Institutes of Health International Working Formulation. Immunophenotypes were then determined by means of an ABC technique with newly generated antibodies that identify fixation-resistant antigens on lymphoid cells. Diffuse small and large cell lymphomas were the most frequently identified subtypes. B-cell-associated antibody, L26, stained a majority of tumor cells in all lymphomas. Although 4KB5 was a less consistent B-cell marker, it stained most lymphomas. Reactive T-cell infiltrates, identified with antibodies MT1, UCHL-1, anti-CD3, and OPD4, varied from slight to intense. MT1 occasionally showed cross-reactivity with neoplastic B cells. No "histiocytic" lymphomas were found, but reactive macrophage infiltrates were identified in many lymphomas with monoclonal antibody KP1. In view of the immunohistochemical results, all lymphomas were believed to be of B-cell origin. Although antibody panels of the type used in this study can be effective in subtyping routinely processed oral lymphomas, careful interpretation is required because of reactive T-cell infiltrates.