Interestingly, blocking prolactin signaling led to activation of the two major prometastatic pathways, the mitogen-activated protein kinase and the TGFβ/Smad signaling pathways, highlighting prolactin as a critical regulator of epithelial plasticity and defining a new role for prolactin as an invasion suppressor hormone in breast cancer [278]. This evidence concerns the gene TGFB1 and breast cancer.