Gastroointestinal stromal tumors (GISTs) are the most common mesenchymal tumors to arise from the gastrointestinal tract. They are characterized by expression of a tyrosine kinase growth factor receptor, also called kit receptor or CD 117. This expression allows unchecked growth of tumor and resistance to apoptosis. These tumors differ immunohistologically and behaviorally from other mesenchymal tumors such as leiomyosarcomas, which do not express kit antigen.