RÉSUMÉ
Gastric adenocarcinoma is the second most common cause of cancer death worldwide, but there are some geographical differences in its incidence. Gastointestinal stromal tumor (GIST) is an uncommon disease with a wide spectrum of aggressive behavior. These two tumors have a distinct pathogenesis. GIST is frequently identified as an incidental lesion found by routine endoscopy or in resection specimens that are removed for other reasons. We report a case of a gastric adenocarcinoma mimicking GIST in a 79-year-old woman. GIST was suggested by endoscopic ultrasonography and computed tomography scanning, but gastric adenocarcinoma was confirmed by gastroduodenoscopic biopsy. We performed a subtotal gastrectomy with Billroth I, lymph node dissection and transverse colon segmentectomy, and a 15.0x7.5x5.5 cm-sized gastric tumor was confirmed pathologically. Immunohistochemistry was positive for carcinoembryonic antigen and focal weakly positive for cytokeratin7 and cytokeratin20.