In contrast, the tumour suppressor Smad pathway has been shown to mediate the prometastatic function of TGF-β in the development of breast cancer bone metastasis (Kang et al, 2005), and dominant negative Smad3 inhibits lung metastasis of breast cancer cells in animal models (Tian et al, 2003). The gene discussed is TGFB1; the disease is breast carcinoma.