title: CD56-positive small round cell tumor: osseous plasmacytoma manifested in osteolytic tumors of the iliac bone and femora.
abstract: Monoclonal gammopathy of undetermined significance does not overexpress cluster of differentiation (CD) 56, but plasma cell myeloma frequently overexpressed it. However, plasma cell leukemia and extramedullary plasmacytoma usually down-regulate CD56 expression. Plasmacytoma, especially 'solitary plasmacytoma of bone', is difficult to diagnose as plasma cell neoplasm, because it occasionally appears similar to other bone tumors, both clinically and pathologically, and is rarely accompanied by monoclonal protein in the serum or urine. The present case was a patient with an osteolytic 'small round cell tumor' of the iliac bone, which also invaded the femora. An immunohistopathological finding of CD56 expression played a key role in making a diagnosis. The definitive diagnosis of plasmacytoma was made based on the electron microscopic findings. The plasma cells which infiltrated her sternum showed the same restriction to kappa light chain expression in their cytoplasms as that of the iliac bone tumor cells, but did not express CD56. Locally infiltrating osteolytic bone tumors should be examined for surface immunoglobulin light chains as well as CD56 expression when plasmacytoma is suspected.
authors.affiliation: Hematology Division, National Cancer Center Hospital 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan. tkouno@ncc.go.jp
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kouno
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Toru
authors.initials: T
authors.lastname: Umeda
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Beppu
authors.forename: Rie
authors.initials: R
authors.lastname: Kojima
authors.forename: Kim
authors.initials: K
authors.lastname: Sungwon
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Kensei
authors.initials: K
authors.lastname: Tobinai
authors.forename: Tadashi
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Matsuno
mesh_terms: D000328:Adult; D001859:Bone Neoplasms / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology; D019002:CD56 Antigen / Q000096:biosynthesis*; D005260:Female; D005269:Femur; D006801:Humans; D007085:Ilium; D008279:Magnetic Resonance Imaging; D010954:Plasmacytoma / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology
chemical_list: D019002:CD56 Antigen