Extramedullary plasmacytoma of the mediastinum.

A case of extramedullary plasmacytoma originating from the upper mediastinum is described. Its pathologic, cytologic and immunohistopathologic findings were distinctive. The neoplastic cells had dense bodies in the cytoplasm. Neither M-protein in the serum nor Bence Jones protein in the urine was detected. However, cellular IgG, having a lambda-type light chain was shown, by immunohistochemical staining following trypsin digestion, to be present in the tissue sections.