Syndecan-1 along with the other three syndecan proteins is present in the varied components of the tumor microenvironment: fibroblasts, inflammatory tumor immunity-associated cells, vessels, and extracellular matrix. Epithelial and non-epithelial tumors may show stromal syndecans. The main relevance of stromal syndecans as tumor biomarker resides in the relationships to tumor features such as type and differentiation as well as to prognosis.