Stem cell factor (SCF, also called Steel factor or Kit ligand) is a dimeric molecule that exerts its biological functions by binding to and activating the receptor tyrosine kinase c-KIT or CD117 (RTK class III, PDGF receptor family). It is also classified as cytokine receptor. Activation of c-Kit leads to its autophosphorylation and initiation of signal transduction. Signaling proteins are recruited to activated c-Kit by certain interaction domains (e.g., SH2 and PTB) that specifically bind to phosphorylated tyrosine residues in the intracellular region of c-Kit. It is expressed by fibroblasts and endothelial cells throughout the body, and activation of c-Kit signaling has been found to mediate cell survival, migration, and proliferation depending on the cell type. Signaling from c-Kit is crucial for normal hematopoiesis, pigmentation, fertility, gut movement, and some aspects of the nervous system. Deregulated c-Kit kinase activity has been found in a number of pathological conditions, including cancer and allergy.