TGFβ has two faces in breast cancer: it can play the role of tumor suppressor to inhibit epithelial cell cycle progression and promote apoptosis during early tumor growth, whereas it also acts as an oncogene that regulates the immune system and the tumor microenvironment to promote the epithelial-to-mesenchymal transition at late stages (reviewed in ref. 46). Here, TGFB1 is linked to breast cancer.