The c-kit proto-oncogene is the cellular homologue of the feline sarcoma v-kit oncogene. It encodes a type III transmembrane receptor tyrosine kinase also known as CD117 or stem cell factor receptor (SCFR). c-Kit signaling is activated when a ligand known as steel factor or stem cell factor (SCF) binds to the receptor. Interactions between specific phosphotyrosine residues of activated receptor tyrosine kinases (RTKs) and Src homology 2 (SH2) domains define cellular growth and differentiation signals. It has been reported that SCF stimulates the association of the p85 subunit of PI3K with the phosphorylated tyrosine-721 residue within wild type kit. Subsequently, PI3K contributes to the activation of Akt and JNKs. c-Kit is necessary for the development of hematopoietic progenitors, mast cells, germ cells, melanocytes, and the interstitial cells of Cajal (ICC). Oncogenic c-kit mutations have been implicated in neoplasms arising from these stem cell lineages, such as gastrointestinal stromal tumor (GIST). The mature, phosphorylated form of c-Kit is a glycosylated protein with a molecular weight of ~145kD, while the immature form is ~125kD.