Specifically, we address (i) the dual role of TGF-β signaling in EMT and MET; (ii) TGF-β dynamic signaling; (iii) the functional difference of TGF-β secreted by exosomes; and (iv) the regulatory effects of tumor microenvironment (TME) – particularly by cancer-associated fibroblasts – on TGF-β signaling activities and its functions. The gene discussed is TGFB1; the disease is cancer.