KIT and gastrointestinal stromal tumor: Most GISTs are diagnosed on the basis of the immunohistochemical demonstration of the expression of KIT (CD117, stem cell factor receptor), a type-III tyrosine kinase receptor encoded by the protoncogene c-KIT, which, therefore, has evidential value in the diagnosis of GIST, which is otherwise difficult to distinguish from other GI mesenchymal neoplasms.