c-Kit, also known as CD117 and stem cell factor receptor, is a 145 kDa transmembrane tyrosine kinase encoded by the c-Kit proto-oncogene. c-Kit acts to regulate a variety of biological responses including cell proliferation, apoptosis, chemotaxis and adhesion. Ligand binding to the extracellular domain leads to autophosphorylation on several tyrosine residues within the cytoplasmic domain, and activation. c-Kit mutations correlate with tumor growth and progression in a variety of cancers including mast cell disease, gastrointestinal stromal tumor, acute myeloid leukemia, Ewing sarcoma, and lung cancer. Phosphorylation at tyrosine 703 of c-Kit allows binding of Grb2 and activation of the Ras-Raf-ERK1&2 signaling pathway.