Transforming growth factor b (TGF- b) is a member of a large family of proteins that play key roles in the control of growth and proliferation of cells. TGF-b initiates signaling by binding to the type I receptor (TbR-I) on the cell surface in conjunction with the type II receptor (TbR-II) to form a complex. TbR-I and TbR-II are both serine/threonine kinase receptors, whereby TbR-I is phosphorylated by TbR-II, thereby activating TbR-I. TbR-I activates a signal transduction cascade through phosphorylation of specific members of the Smad family of transcription factors. Stimulation of Smad proteins allows them to translocate from the cytoplasm to the nucleus leading to the activation or repression of a number of genes.

The key position that the TGF-b pathway plays in the maintenance of cellular homestasis makes it a prime target of cancer cells. The disregulation of TGF-b is one of the primary steps in the process of tumorgenesis and metastasis. The underlying mechanisms have yet to be elicudated in a number of cancers involved in the TGF-b pathway and the use of inhibitors to TGF-b may serve as a useful tool to unravel this process.