c-Kit is a transmembrane tyrosine kinase encoded by the cKit 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. Mutations in c-Kit have been found to be important for tumor growth and progression in a variety of cancers including mast cell diseases，gastrointestinal stromal tumor，acute myeloid leukemia，Ewing sarcoma and lung cancer. Phosphorylation at tyrosine 721 of c-Kit allows binding and activation of PI3 kinase.