These findings mark Syndecan-1 as an important contributor to CSC stemness, and are in accordance with the observed upregulation of Syndecan-1 in breast cancer [34,35] and resistance of Syndecan-1-deficient mice to experimentally-induced breast cancer [36-38]: CSCs are thought to be enriched in the SP, which is responsible for increased therapy resistance [3,21]. Here, SDC1 is linked to breast cancer.