Lack of Expression of c-kit Protein (CD117) in Mesenchymal Tumors of the Uterus and Ovary

c-kit is a proto-oncogene that codes for a transmembrane tyrosine kinase receptor (CD117). The gene product KIT is constitutively overexpressed in mastocytosis and gastrointestinal stromal tumors. Recently the use of the tyrosine kinase inhibitors, such as STI-571, has resulted in the successful treatment of bcr-abl-positive leukemias and gastrointestinal stromal tumors. In gastrointestinal stromal tumors, immunostaining for c-kit is diffusely positive. Because the expression of c-kit in mesenchymal tumors of the uterus and ovary has not been previously studied, we evaluated its expression in 38 of these tumors by immunohistochemistry. The number of positive labeled/total tumors were as follows: 0/8 malignant mullerian mixed tumors, 4/7 ovarian fibrosarcomas, 0/1 clear-cell ovarian sarcoma, 0/4 uterine leiomyosarcomas, 1/10 low-grade endometrial stromal sarcomas, 0/2 high-grade endometrial stromal sarcomas, and 3/6 endometrial stromal nodules. In all positive cases, no more than 5% of the cells were labeled. In conclusion, unlike gastrointestinal stromal tumors, mesenchymal tumors of the uterus and ovary rarely express c-kit. Therefore, it is unlikely that patients with these tumors will benefit from treatment with the currently available tyrosine kinase inhibitors.