Extramedullary plasmacytoma of skeletal muscle. A case report with immunocytochemistry and ultrastructural study.

An uncommon origin of a rare tumor is described in a 60-year-old white man. Extramedullary plasmacytoma was localized in the left biceps muscle. Tumor immunostaining corresponded with immunocharacterization of the atypical midgamma band on electrophoresis or the serum monoclonal M protein of IgG kappa. The latter disappeared 6 months after the operation. The diagnosis was confirmed ultrastructurally.