Transforming growth factor beta (TGFB) suppresses early stages of tumorigenesis, but also contributes to migration and metastasis of cancer cells. A large number of human tumors contain mutations that inactivate its receptors, or downstream proteins such as Smad transcription factors, indicating that the TGFB signaling pathway prevents tumor growth. We investigated the effects of TGFB inhibition on liver tumorigenesis in mice.