Smad3 is a central signaling molecule of TGF-β1, inducing epithelial-to-mesenchymal transition (EMT), during which early stage tumors are converted into invasive malignancies.7 Overexpression of Smad3 promoted metastasis in mice injected with human metastatic breast cancer cells (MCF10CA1a), but a COOH-terminally truncated dominant negative mutant of Smad3 suppressed cell metastasis.8 Here, SMAD3 is linked to breast cancer.