Gastric submucosal tumors (SMTs) are occasionally observed on gastrointestinal endoscopy. Ectopic pancreas is a rare but important entity. In this case report, we describe the case of a 21-year-old female patient who presented with frequent vomiting after meals and was found to have a giant gastric SMT causing gastric outlet obstruction. Upper gastrointestinal endoscopy, radiography, plain computed tomography (plain CT), contrast-enhanced computed tomography (CE-CT), abdominal ultrasound and abdominal magnetic resonance imaging (MRI) showed a cystic lesion in the gastric antrum. The lesion was completely removed through tumor resection via laparotomy on the serosal side, without damaging the gastric mucosa and without any leakage of fluids from the lesion. Pathological examination revealed that the lesion was ectopic pancreas, Heinrich type II with no malignancy. The fluid in the cystic tumor had high levels of carcinoembryonic antigen (CEA) and Carbohydrate Antigen 19-9 (CA19-9). Immunostainings of CEA and CA19-9 were positive.
