Syndecan-1 (SDC1), also named CD138, is an integral membrane protein. It participates in cell proliferation, cell migration and cell-matrix interactions via its receptor for extracellular matrix proteins. It is a heparan sulfate proteoglycan expressed on the surface of, and actively shed by, myeloma cells. Altered syndecan-1 expression has been detected in several different tumor types. SDC1 was regarded as a useful marker for labeling normal and neoplastic plasma cells and plasmacytoid lymphomas.