Furthermore, the overexpression of this cell surface proteoglycan syndecan 1 (SDC1) in senescent cells after irradiation of human breast cancer is the result of autocrine action in TGF-β via the Smad pathway and the transcription factor Sp1 and does not involve classical aging pathways, such as p53 or p38 MAPK-NF-kB [164]. Here, TP53 is linked to breast carcinoma.