Solitary extraosseous plasmacytoma.

Plasma cell neoplasms are characterized by a neoplastic plasma cell lineage which produces a monoclonal immunoglobulin. These neoplasms can present as a single lesion (solitary plasmacytoma) or as multiple lesions (multiple myeloma). Solitary plasmacytomas most frequently occur in bone (plasmacytomas of bone), but can also be found outside bone in soft tissues (extramedullary plasmacytomas).