SDC1 and breast cancer: For example, as the most abundant cells in the microenvironment, fibroblasts can use cytomembrane syndecan-1 to cooperate with matrix molecules, such as heparan sulfate (HS) and fibroblast growth factors (FGFs), to combine with cognate receptors, such as FGFR, on the surface of breast cancer cells and assemble into signaling complexes to promote breast cancer cell proliferation via Wnt signaling pathways [39, 40].