Multiple Myeloma

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Radiographs of the left knee show a poorly marginated lytic bone lesion in the distal femur.  The patient eventually had a pathologic fracture throught that lesion (also shown). Lytic thoracic spine lesions were also doccumented by CT.  Peripheral blood smear was loaded with plasma cells.  These cells stain positive for CD 138 (inset).  SPEP revealed an IgG Kappa spike. Findings are consistant with multiple myeloma. 

CD 138, Syndecan 1,  is a protein which in humans is encoded by the SDC1 gene. Syndecans mediate cell binding, cell signaling, and cytoskeletal organization.  Syndecans are single transmembrane domain proteins that are thought to act as coreceptors, especially for G protein-coupled receptors. These core proteins carry three to five heparan sulfate and chondroitin sulfate chains which allow for interaction with a large variety of ligands including fibroblast growth factors, vascular endothelial growth factor, transforming growth factor-beta, fibronectin and antithrombin-1.  Altered syndecan-1 expression has been detected in several different tumor types. It is a useful marker for plasma cells

O'Connell FP, Pinkus JL, Pinkus GS . "CD138 (syndecan-1), a plasma cell marker immunohistochemical profile in hematopoietic and nonhematopoietic neoplasms". Am. J. Clin. Pathol. 121 (2): 254–63