Immunohistochemical and ultrastructural heterogeneity of gastrointestinal stromal tumors

Aims and methods-Digestive stromal tumors are the most frequent undifferent iated mesenchymal tumors. The prognosis of these tumors is difficult to pre dict and the histogenesis is still subject to controversy. However, the fre quent and specific expression of CD 117 (c-kit) by these tumors could sugge st an origin from interstitial cells of Cajal. The aim of this study was to analyse the histological and immunohistochemical characteristics of 46 dig estive stromal tumors surgically resected with comparaison of CD34 and CD 1 17 expression in these tumors. Sixteen tumors were analyzed on electron mic roscopy. Results-Sixty three and 74% of the stromal tumors were positive for CD 117 and CD34 respectively. While CD 117 expression was similar in all locations , on the contrary, there was a decreasing gradient of CD34 expression betwe en gastric (87%) and jejunal (33%) tumors. All tumors with skeinoid fibers expressed CD 117. Focal expression of smooth muscle actin was noted in 43% of the cases. The ultrastructural study showed no correlation with the immu nohistochemical results. Conclusion-Digestive stromal tumors show an immunophenotypic and ultrastruc tural heterogeneity. CD 117 expression is frequent, but not constant.