[An autopsy case of extramedullary plasmacytoma with systemic dissemination 2 years after the onset of a localized tumor in the nasal cavity].

A 73-year-old male was admitted because of a localized tumor in the nasal cavity, which was suspected to be malignant lymphoma by biopsy specimens. Laboratory findings were within normal limits except for small amounts of M protein (IgG-lambda) in the serum. The patient was successfully treated by radiotherapy, with the disappearance of both the tumor and M protein. Two years after the onset, however, a solid tumor was observed in the soft tissue, followed by rapid systemic dissemination. An increase in M protein was obvious, and the biopsy specimens disclosed plasmacytoma. The patient died three months after admission, and post-mortem examinations revealed a diffuse infiltration of plasmacytes predominantly in the soft tissues.