CD117, also known as c-Kit, encodes a receptor tyrosine kinase that is activated by its ligand stem cell factor and plays an important role in vital functions such as homeostasis and melanogenesis. CD117 is a protooncogene. Mutations and overexpression are associated with several types of cancer, including gastrointestinal stromal tumors (GIST), mast cell disease, acute myeloid leukemia (AML), small cell lung cancer (SCLC) and Ewing’s sarcoma. Expression is found in a variety of normal and abnormal cells, such as hematopoietic stem cells, melanocytes, mast cells, germ cells and basal cells of the skin.