Extragastrointestinal Stromal Tumors: A Clinicopathologic And Immunohistochemical Study Of 16 Cases

BACKGROND & AIMSExtragastrointestinal stromal tumors (EGISTs) develop outside of the digestive tract especially in the soft tissues of the abdomen and retroperitoneum, and have no or little connection to the abdominal wall or serosal surface of the gastrointestinal tract. They account for 4% of gastrointestinal stromal tumors (GISTs). The term GISTs was first offered in 1983 by Mazur and comprised most gastrointestinal tract tumors. In the past few years revolutionary changes in our knowledge about GISTs resulted in much attention to different topics related to them. As a result of their rarity, thefeatures of the EGISTs have not been fully elucidated. They are usually misdiagnosed as other abdominal tumors because of non-specific symptoms. The aim of this study is to investigate the clinicopathologic features, immunohistochemical speciality, cellular origin and prognostic factors of the EGISTs.MethodsThe clinical data of 16 patients were retrospective analyzed. The morphologic characteristics of EGISTs were observed by light microscopy, and the expression of CD117, CD34, smooth muscle actin (SMA), Desmin, S-100 and muscle common actin (HHF-35) were detected by Envision immunohistochemical method.ResultsEGISTs occurred in 11 men and 5 women. The patients ranged in age from 38 to 75 years (mean 57.1 years, median 55 years), and 11 patients (68.8%) were older than 50 years. Abdominal mass (7 cases) was the most common presenting symptom, followed by bellyache (6 cases), abdominal distention (2 cases) and defecation change (2 cases). One case was incidentally found during otherlaparotomy. Eight cases arose principally from the retroperitoneum, 5 cases from the omentum and 3 cases located at the mesentery. The tumor size ranged from 1.0 to 15.0 cm (mean 8.0 cm). Histologically, there were 13 cases of mainly spindle cell type, 1 case of mainly epithelioid cell type and 2 cases of mixed cell type. Thirteen cases were differentiated as malignant tumors, 2 cases as benign tumors and 1 case as borderline malignant tumors. Immunohistochemical CD117 diffusively strong expression was documented in 13 cases (81.3%). Two cases without CD117 results were included, so the real positivity was 92.9%. CD34 diffusively strong expression or predominant positivity was seen in 12 cases (75%), SMA positivity in 4 cases. Two cases showed S-100 and Desmin reactivity respectively and one had HHF-35 positive tumor cells.ConclusionEGISTs predominantly occur in the middle and old age patients, more common in malignant cases. CD117 and CD34 were the specific and sensitive antibody in diagnosis of EGISTs. Immunohistochemistry plays an important role in the pathological diagnosis and differential diagnosis. EGISTs wereidentical by histological and immunohistochemical features with GISTs, and they may all arise from the multipotential mesenchymal stem cells of mesoderm. EGISTs have various clinical behavior, and the parameters used for predicting the prognosis of GISTs may not be completely suitable for EGISTs evaluation.