TGFB1 and breast cancer: For example, Stope et al. found that ESR1 but not ESR2 inhibited TGF-β1 activation in breast cancer cells [18] while others found that both ESR1 and ESR2 suppressed TGF-β1 signaling by associating with and acting as a transcriptional corepressor for SMAD3 [19, 20].