Gastrointestinal stromal tumor (GIST) is the most common type of mesenchymal tumor in the gastrointestinal tract. A large tumor size often means a poor prognosis. This report presents a case of a large exophytic GIST with cyst change, for which the outcome of favourable prognosis was unexpected. A 78-year-old male presented with abdominal distension and a poor appetite, and was primarily diagnosed with a pancreatic mass. Abdominal ultrasonography, computed tomography and magnetic resonance imaging revealed a tumor in the body of the pancreas, which was closely attached to the gastric wall. Surgery was performed to excise the tumor. The tumor originated from the gastric cells and was ~17×15×16 cm in size. A diagnosis of GIST was confirmed by histomorphological and immunohistochemical findings. According to the postoperative findings, the tumor was classified to be in the high-risk group, for which the suggested treatment is imatinib. However, the patient was not treated with imatinib and, three years following surgery, the patient is alive with no evidence of tumor recurrence.
Keywords: cystic change; exophytic gastrointestinal stromal tumor; prognosis.