CD117, also known as c-Kit, is a cytokine receptor expressed on the surface of hematopoietic stem cells (HSC) as well as other cell types. CD117 is a receptor tyrosine kinase type III, which binds to stem cell factor. When this receptor binds to stem cell factor, it forms a dimer that activates its intrinsic tyrosine kinase activity, which in turn phosphorylates and activates signal transduction molecules that propagate the signal in the cell. Signaling through CD117 plays a role in cell survival, proliferation, and differentiation. HSC, multipotent progenitors (MPP), and common myeloid progenitors (CMP) express high levels of CD117. Activating mutations in this gene are associated with gastrointestinal stromal tumors, testicular seminoma, mast cell disease, melanoma, acute myeloid leukemia, while inactivating mutations are associated with the genetic defect piebaldism.