This catabolic phenotype is complemented by the overexpression of the cell surface heparan sulfate proteoglycan syndecan-1, a poor prognostic factor for breast cancer development that was found to be regulated by transforming growth factor-β (TGF-β) through the Smad pathway and the transcription factor Sp1 in an autocrine and paracrine manner. Here, SP1 is linked to breast cancer.