Clinicopathological and immunohistochemical features of extragastrointestinal stromal tumors: report of two cases.

CD117 (c-kit proto-oncogene protein product) is expressed in most gastrointestinal stromal tumors (GISTs) and plays a crucial role in the pathogenesis and treatment of this disease. However, the clinicopathological and immunohistochemical features of CD117-positive mesenchymal tumors without connection to the gastrointestinal tract, known as extragastrointestinal stromal tumors (EGISTs), are not well documented because these tumors are rare. We describe the clinicopathological and immunohistochemical features of two cases of EGIST and compare them with those of GIST. Of the 1855 abdominal or esophageal tumors resected during the past 10 years at our hospital, 23 were GISTs and 2 were EGISTs. The clinicopathological or immunohistochemical characteristics do not seem to differ remarkably between EGISTs and GISTs. Although rare, CD117 positivity should be tested in abdominal mesenchymal tumors that have no connection to the gastrointestinal tract. The clinicopathological features of CD117-positive abdominal mesenchymal tumors may not depend on whether the tumor is connected to the gastrointestinal tract.