Transforming growth factor-alpha (TGF-α) a member of the epidermal growth factor (EGF) family that is expressed in normal epithelial cells, monocytes, macrophages, brain cells, keratinocytes, and cancer cells. TGF-α binds EGF receptor (EGFR) and activates tyrosine kinase signaling. In epidermal and epithelial cells, this results in proliferation and differentiation. TGF-α is not structurally or genetically related to TGF-β, and the two ligands act through different signaling pathways. In vitro, TGF-α was shown to stimulate anchorage-independent growth (Singh & Coffey).