Prominent plasmacytic differentiation in the recurrence of a parotid immunocytoma. A morphologic and immunohistochemical study.

We report and discuss a case consisting of 2 lesions that developed at different times in the same parotid gland. Although the first lesion showed morphologic features similar to those of the benign lymphoepithelial lesion, a monotypic IgM/K pattern was also revealed by the immunoperoxidase method in its lymphoid infiltrates. Thus, on cytologic grounds, the first lesion was classified as lymphoplasmacytic immunocytoma (according to Kiel criteria). In the second lesion, which recurred 3 years later, the prominent feature was a marked predominance of plasma cells with the same monoclonal IgM/K as the preceding lymphoma. These findings suggests that a B-lymphomatous cell monoclone may undergo morphologic maturation along the lineage of its competence. Secondly, they indicate that every case of benign lymphoepithelial lesion of the salivary glands should undergo thorough immunologic evaluation to exclude the possibility of signs of precocious lymphomatous transformation.