histological and immunological evaluation of gastrointestinal stromal tumors

background: gastrointestinal stromal tumors (gists) constitute the majority of gastrointestinal mesenchymal tumors. they usually express a proto-oncogen protein called cd117 detected by immunohistochemistry. this study investigated the differentiation of gists as well as the risk of aggressive behaviors in gists from surgically-treated patients in university affiliated hospitals.   methods: the clinicopathologic, histomorphologic and immunohistochemical features of 36 gists of patients referring to two large general hospitals in the last 13 years were examined.   results: the gists occurred in 36 patients (41.6% male and 58.4% female) aging 15 to 89 years. 50% of the cases were in the stomach, 30% in the small intestine and the remainder in the colon and mesenter. the diameters of tumors were 0.7 to 30 cm and mostly (60.6%) more than 5. 85% of tumor cells were spindle, 14% epithelioid, and the remainders were mixed. 36.1% of tumors showed mitotic counts > 5/50 hpf and 11.1% less than 5/50hpf. 33.3% of the tumors showed necrosis. 8 tumors had malignant behavior during 13-yrs follow up. immunoreactivity for c-kit, sma, chromogranin, synaptophysin, desmin and s100 were 83.3%, 69.4%, 44.4%, 41.6%, 50% and 0%, respectively. the decreasing rank order of differentiation forms were neural, smooth muscle, dual and null. most of our tumors were in high risk group and most of the high risks were intestinal with neurogenic differentiation.   conclusion: immunostaining including c-kit is necessary to study the differentiation of gastrointestinal stromal tumors. iran j med sci 2006; 31(1): 14-17.   keywords ● gastrointestinal stromal ● tumor ● histology ● immunohistochemistry ● c-kit