Transforming growth factor-beta (TGF-β) plays a dual role in hepatocellular carcinoma (HCC), acting as a tumor suppressor in early stages by inducing cell cycle arrest and apoptosis, and as a promoter in advanced stages by fostering tumor progression, epithelial–mesenchymal transition (EMT), and metastasis. The gene discussed is TGFB1; the disease is hepatocellular carcinoma.