Introduction. Gastrointestinal stromal tumors (GIST) are tumors of mesenchymal origin which originate from the walls of gastrointestinal system (GIS) organs. Aim. In this case report we aim to discuss the clinical, labaratory and radiological presentation of distal duodenal GIST as a rare and overlooked cause of life-threatining GIS bleeding. Description of the case. A 76-year-old male patient was presented to the emergency department with massive gastrointestinal bleeding. Computerized tomography revealed a mass soft tissue density of 4x4cm at the level of the 3-4th segment of the duodenum. At the endoscopy, there was a deep ulcer in the proximal part of the 3rd segment of the duodenum with a diameter of 2 cm with a bleeding vessel protruding into the lumen. After endoscopic treatments, biopsies were taken from the edges of the ulcer. Histopathological examination revealed a sheet-like infiltration composed of mildly pleomorphic cells with oval-spindle nuclei and abundant eosinophilic cytoplasm in the duodenal lamina propria, as the patient was diagnosed of GIST. Conclusion. GIST and its clinical, labaratory and radiological presentation should be kept in mind in the approach to massive duodenal GIS bleeding.
