Also referred to as “steel factor” or “c-kit ligand,” CD117 isthe tyrosine-kinase receptor for stem cell factor (SCF).Although its receptor is found in various cells, C-kit is apolypeptide that activates bone marrow progenitors ofcertain blood cells. Gastrointestinal Stromal Tumours(GISTs) are likely caused by C-kit mutations in the interstitialcells of the Cajal in the digestive system.The CD117 antibody interacts with mast cells, melanocytes,bone marrow stem cells, germ cells, interstitial cells ofCajal, and breast epithelium. Although this receptor ispresent on a wide range of tumour cells, including thyroidfollicular and papillary carcinoma, adenocarcinomas fromthe endometrium, lung, ovary, pancreas, and breast;malignant melanoma, endodermal sinus tumour, andsmall-cell carcinoma, it has proven especially helpful indistinguishing between smooth-muscle tumours andgastrointestinal stromal tumours (GIST) and Kaposi’ssarcoma.