Syndecans are cell surface proteoglycans that mediate cell-matrix and cell-cell adhesion and act as co-receptors for some growth factors. Although little is known regarding the role of syndecans in disease, emerging evidence indicates that they play an important role in regulating the behavior of tumor cells. It has been demonstrated that expression of syndecan-1 is essential for maintaining epithelial morphology in vitro and that some tumors growing in vivo reduce or lose their expression of syndecan-1 during their transformation to a malignant state. In addition, there is now direct evidence that syndecan-1 inhibits tumor cell invasion within the extracellular matrix. Human myeloma cells that do not express syndecan-1 will readily invade into type I collagen gels. However, following their transfection with a cDNA for syndecan-1, these cells are rendered non-invasive. These studies indicate that expression of syndecan-1 supports a non-invasive phenotype and that loss of syndecan-1 expression may be necessary prior to the metastasis of some tumors. © 1995, FCCA(Forum: Carbohydrates Coming of Age). All rights reserved.