During cancer progression, transforming growth factor-β (TGF-β) sequentially activates SMAD2/3 and SMAD4 through activation of TGF-β type I receptor (TβRI), and SMAD4 enters the nucleus and promotes the expression of oncogenes, leading to epithelial-mesenchymal transition (EMT) [15]. The gene discussed is SMAD4; the disease is cancer.