Fig. 1. The dual role of TGF-β signaling in tumor progression.
TGF-β induces apoptosis and inhibits the proliferation of normal or nontransformed cells but loses its growth inhibitory properties as cells progress to later stages of tumorigenesis. In later stages of tumor progression, TGF-β is actively secreted by cancer cells or stromal cells and acts as a tumor promoter by promoting EMT, cancer cell migration and invasion, and the formation of an immunosuppressive tumor microenvironment. EMT, epithelial-mesenchymal transition.