KIT, also named as SCFR, c-Kit and CD117, is a transmembrane tyrosine kinase encoded by the cKit proto oncogene. It is a type 3 transmembrane receptor for MGF (mast cell growth factor, also known as stem cell factor). KIT acts to regulate a variety of biological responses including cell proliferation, apoptosis, chemotaxis and adhesion. Ligand(SCF) binding to the extracellular domain leads to autophosphorylation on several tyrosine residues within the cytoplasmic domain, and activation. Phosphorylation at tyrosine 721 of KIT allows binding and activation of PI3 kinase. Loss of expression of KIT appears to be associated with progression of some tumors (melanoma) and autocrine/paracrine stimulation of the kit/SCF system may participate in human solid tumors such as lung, breast, testicular and gynecological malignancies. Mutations in 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.