Plasmacytoma with oncocytic changes. A case report.

: In this report we will document a readily identifiable, morphologic variant of plasma cells in an extramedullary plasmacytoma. Ultrastructurally, the tumor cell cytoplasm was almost completely occupied by proliferating mitochondria. Localized areas of endoplasmic reticulum were, however, also noted. The light microscopic features of this tumor (i.e. foamy eosinophilic cytoplasm) and special staining (methyl green pyronin (MGP) characteristics were compatible with the fine-structural details of these cells. The usefulness of obtaining a clinical/pathological correlation for the behavior of this type of tumor is discussed.