The clinicopathologic features of 136 gastrointestinal stromal tumors were analyzed. The tumors occurred in 60 women and 76 men, ranging in age from 19 to 88 years (median 59 years, mean 59.2 years). Sixty-one cases arose from stomach, 38 from small intestine and 11 from colon or rectum. Abdominal cavity was indicated as tumor site in 10 cases, but the extragastrointestinal origin using strict criteria was not proved. Four locally recurrent cases and 12 metastatic samples were also included. The primary and recurrent tumors ranged in size from 0.5 to 30 cm (mean 8.3 cm). The large number of high-grade cases (85 of 112 classifiable) is alarming and emphasize the importance of oncology care. Histologically, ninety-two cases were classified as spindle cell while 11 as epithelioid GIST. Mixed cellularity was seen in 33 cases. Skeinoid fibers were present in 14 and coagulation necrosis in 40 primary cases. Ulceration observed by microscopic examination was common (36 of 110 cases, 32.7%), explaining the clinically frequently observed gastrointestinal bleeding. Unusual histological features such as stromal hyalinization and nuclear palisading were present in 30 and 27 cases, respectively. Immunohistochemical CD117 (c-kit) positivity was documented in 133 cases. Three cases with CD117 negative results were included, because their morphology was most consistent with GIST and immunohistochemical reactions excluded the possibility of other neoplasms. CD34 positivity was seen in 70%, alpha-smooth muscle actin positivity in 39.6% of examined cases. Only one case showed desmin reactivity and seven had S100 positive tumor cells. For h-caldesmon 39 cases proved to be positive (60.9% of the tested cases).
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