KIT and gastrointestinal stromal tumor: CD117, commonly known as c-kit or stem cell factor receptor, is a “KIT-proto-oncogene receptor tyrosine kinases” expressed in non-malignant cells, including hematopoietic stem cells (HSCs), melanocytes, mast cells, and breast epithelium, but not on plasma cells, gastrointestinal stromal tumors, acute leukemias, myelodysplastic syndromes, monoclonal gammopathies and MM.