الفهرس 
INTRODUCTION AND AIM OF WORKOnly 14 pages are availabe for public view
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Abstract
Gastrointestinal stromal tumors (GIST) are rare tumors of the gastrointestinal (GI) tract that arise from primitive mesenchymal cells. GISTs occur throughout the GI tract. They thought to originate from interstial cell of Cajal but recently it is proved to originate from mesenchymal progenitor cells. The pathogenesis of GIST is dependent on abnormal c-kit function. Forty mesechymal stromal tumors involving GIT and omentum were studied histologically and histochemically using ordinary hematoxylin and eosin, Masson Trichrome stain and PAS stain. Thirty five cases were immunostained with CD117 and selected cases were immunestained by viementin, desmin, S100 and SMA. The studied cases showed wide variability in histological and histochemical features leading to overlapping with smooth muscle tumors, nerve sheath tumors. The inflammatory fibrous tumor differentiated by Masson trichrome stain then assured by c-Kit negativity. Twenty five cases were c-Kit positive and diagnosed GISTs. The remaining ten cases are c-Kit negative. Three of them were viementin positive, desmin negative and S100 negative and considered c-Kit negative GISTs. Four cases of these c-Kit negative tumors were desmin positive and accordingly diagnosed as smooth muscle tumors. One case is inflammatory fibrous tumors and two endoscopic blocks were finished. The c-Kit positive cases were classified according to Fletcher., et al 2002 depending on tumor size and number of mitoses/ 50HPF for risk assessement into three cases of low risk, twelve caes of intermediate cases, and ten cases with high risk.