A Case of Gastrointestinal Stromal Tumor of Duodenum Diagnosed before Operation

A gastrointestinal stromal tumor (GIST) of the duodenum in a 51-year-old male is reported. The patient presented with a history of repeated tarry stools and was admitted to our hospital. An elevated lesion with ulceration was found in the third portion of duodenum as a result of various types of examinations. Biopsy revealed a GIST originating in the duodenum, and partial duodenectomy was performed. The surgical specimen was a submucosal tumor, 38×37×30 mm in size, with a clear border and central necrosis. Pathological examination revealed dense fascicular proliferation of spindleshaped tumor cells in a bundle and 2-4 nuclear divisions in 10 HPFs. Since immunohistochemical studies revealed tumor cells with a positive pattern for vimentin and CD34, and negative pattern for desmin, α-smooth muscle actin, HHF-35, and S-100 protein, we made a diagnosis of malignant gastrointestinal stromal tumor, uncommitted type. GISTs originating in the duodenum are rare and more malignant than GISTs originating at other sites in the digestive tract, and therefore careful follow-up may be required.