KIT and gastrointestinal stromal tumor: Cases of simultaneous occurrence of a GIST with a well-differentiated NEC have been reported at present, and CD117 is positive, so the pathologists need to pay more attention to the differentiation between GISTs and NEC.[16,17] In the NEC, immunopositive for CK, CgA, and Syn.[18] In the malignant mesothelioma, the immunocytochemical for CK5/6 and EMA are positive, but CD117 is not expression.