CD117 (mast/stem cell growth factor receptor, SCFR, KIT oncogene) is a protein tyrosine kinase receptor for the cytokine KITLG/SCF. Activation regulates apoptosis and cell proliferation, differentiation, chemotaxis, and adhesion. Altered forms are associated with cancer. CD117 is expressed on hematopoietic stem cells and progenitor cells and some nonhematopoietic cells such as mast cells, melanocytes, germ cells, interstitial cells of Cajal, skin adnexa epithelial cells, and some cerebellar neurons and in breast tissue. It is also expressed in tumors of these cell types. Staining is used primarily to identify gastrointestinal stromal tumors and also small-cell lung carcinoma, acute myelogenous leukemia, chronic myelogenous leukemia, breast carcinoma, glioblastoma, and melanoma. References: Int J Biochem Cell Biol. 2007;39(11):1995-1998. doi: 10.1016/j.biocel.2006.12.005; Appl Immunohistochem Mol Morphol. 2005;13(3):205-220. PMID: 16082245; Oncogene. 2005;24(26):4271-4280. doi: 10.1038/sj.onc.1208587; Hum Pathol. 2002;33(12):1182-1187. doi: 10.1053/hupa.2002.129199