Immunoperoxidase characterization of pharyngeal plasmacytoma

Extramedullary plasmacytomas (EMPs) are plasma cell neoplasms that most frequently arise along the upper airways and often do not secrete detectable amounts of M protein at the time of diagnosis. The present report describes the immunohistochemical characterization of an EMP in a young woman. The unlabeled peroxidase-antiperoxidase method was employed to demonstrate cytoplasmic immunoglobulin determinants in routinely processed, paraffin-embedded tissue. Only kappa light chain and lambda heavy chain determinants were found in the cytoplasm of the neoplastic plasma cells; essentially identical results were found in both initial and recurrent lesions separated by a 16-month interval. This exclusive staining of one light chain type associated with only one heavy chain represents a monoclonal staining pattern that is typical of B-cell neoplasms. Such characterization of EMPs on the basis of cytoplasmic immunoglobulin class and type may provide prognostic information analogous to the classification of multiple myeloma by immunoelectrophoresis.