Syndecan-1 (CD 138) in myeloma and lymphoid malignancies: A multifunctional regulator of cell behavior within the tumor microenvironment

Syndecan-1 is a transmembrane proteoglycan expressed on the surface of tumo r cells of various origins including myeloma, Hodgkin's disease, and certai n human immunodeficiency virus (HIV) associated lymphomas. Functional studi es in myeloma reveal that syndecan-1 may act as a multifunctional regulator of cell behavior in the tumor microenvironment; it mediates cell-cell adhe sion, binding of myeloma cells to type I collagen, and inhibits tumor cell invasion into collagen gels. In addition, syndecan-1 is released from the s urface of myeloma cells and this shed form of the molecule inhibits growth and induces apoptosis of myeloma cells and may modulate myeloma bone diseas e by inhibiting osteoclast formation and promoting osteoblast formation. In view of its effects on tumor cell growth, survival, adhesion and invasion and on bone cell differentiation, syndecan-1 may be an important potentiall y beneficial regulator of myeloma pathobiology. Further studies are needed to define the clinical significance of syndecan-1 in myeloma and to examine its functional significance in other lymphoid malignancies.