CD117, also known as c-Kit, encodes a receptor tyrosine kinase that is activated by its ligand stemm 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 cancer types, including gastrointestinal stromal tumors (GIST), mast cell diseases, acute myeloid leukemia (AML), small cell lung carcinoma (SCLC), and Ewing's sarcoma. Expression is found in a variety of normal and abnormal cells, such as hematopoetic stem cells, melanocytes, mast cells, germ cells, and basal cells of skin. ^1-2