The coexpression of these markers, along with the presence of TFE3 nuclear staining in some cases and negative staining for S100, and cytokeratin and CD117 (c-kit) staining, helps distinguish PEComas from other mesenchymal tumors such as GISTs and leiomyosarcomas [2,13]. The gene discussed is KIT; the disease is mesenchymal cell neoplasm.