[A Case of Intraductal Growth Pattern Gastrointestinal Stromal Tumor of the Stomach That Was Difficult to Diagnose by Biopsy].

The patient, a 76-year-old man, presented to his local doctor's clinic with complaints of fatigue and lightheadedness. Because blood test results indicated anemia, he was referred to our hospital. Upper gastrointestinal endoscopy indicated a type 2 tumor of approximately 5 cm at the top of the gastric corpus. Biopsy results indicated that the lesion was a poorly differentiated adenocarcinoma. Computed tomography showed multiple liver metastases and the patient was diagnosed with stage Ⅳ gastric cancer. After a blood transfusion, chemotherapy with S-1 was started. However, as the patient experienced continued hemorrhage from the primary lesion, treatment was changed to total gastrectomy in order to control the bleeding. The pathologic examination of the resected specimen indicated that the tumor was located in the muscle and subserosal layers. The tumor cells were spindle-shaped, c-kit positive, cytokeratin-negative, and Dog-1 positive. Therefore, a diagnosis of gastrointestinal stromal tumor (GIST) was made. Postoperatively, chemotherapy with imatinib was administered and the patient was alive with no progression of disease 1 year following surgery. Intraductal growth pattern GISTs of the stomach that protrude into the epithelium and exhibit ulceration can be difficult to distinguish from gastric carcinomas. We experienced a case of gastric GIST that was difficult to diagnose preoperatively.