Immunohistochemical markers such as CD34 and CD117 are important for the differentiation of subepithelial lesions such as GIST and leiomyoma, but the application of markers is only possible when an adequate amount of analysis material is available2,6, as occurred in case 2, in which the diagnosis was confirmed only after complete resection of the tumor. The gene discussed is CD34; the disease is gastrointestinal stromal tumor.