Thyroid-gland plasma cell neoplasm (plasmacytoma).

A 61-year-old man with a primary thyroid plasmacytoma was studied. Intracytoplasmic monoclonal immunoglobulin (IgG-kappa) was demonstrated in tissue sections, using the immunoperoxidase technique. After histologic diagnosis of plasmacytoma, serum immunoelectrophoresis revealed a monoclonal component (IgG-kappa). Roentgenographic skeletal survey and bone marrow examination gave normal results. The patient received postoperative therapy with radiation and drugs. As of this writing, he is alive 20 months after diagnosis, without evidence of tumor.