Inclusion of TGF-β signaling inhibitor SB431542 in the growth medium blocked the proliferation of MDA-MB-231 cancer cells without any effect on the HMEC growth suggesting that MDA-MB-231 cells are dependent on autocrine TGF-β signaling for their proliferation but not HMEC (see Figs. 1D & 1E). Here, TGFB1 is linked to cancer.