TGFB1 and breast cancer: When the breast cancer cells (MDA-231, ZR-75-1 or MCF-7) were stimulated with TGFβ(10-10M) and cultured in the presence of 10% FCS the cancer cells induced significant degradation of type I collagen (range 70–80%), whereas minimal degradation was observed in the absence of serum (Fig. 1).