Case Report: Ectopic pancreas mimicking gastrointestinal subepithelial tumors: diagnostic challenges in two surgically confirmed sibling cases.

Background: Ectopic pancreas is a congenital developmental anomaly that may occur in the stomach, duodenum, jejunum, and other gastrointestinal sites. Because its clinical, laboratory, and imaging features are often nonspecific, it may mimic gastrointestinal subepithelial tumors, particularly when presenting as a submucosal, intramural, or wall-based mass. Gastrointestinal stromal tumor (GIST) is often an important preoperative differential diagnosis, but it is not the only diagnostic consideration. Case presentation: We report two biological sisters with pathologically confirmed ectopic pancreas. Case 1 was the younger sister. She was asymptomatic and was found to have a gastric submucosal lesion and an enhancing small intestinal nodule during a routine health check-up. Gastroscopy, endoscopic ultrasonography, and contrast-enhanced computed tomography suggested a gastrointestinal subepithelial tumor, with GIST considered as the leading preoperative diagnosis, and both lesions were surgically resected. Histopathology confirmed ectopic pancreas at both sites. Case 2 was the elder sister. She presented with right upper abdominal pain radiating to the back, low-grade fever, elevated C-reactive protein, and a proximal jejunal wall-based mass on multimodal imaging. GIST could not be excluded before surgery. Laparoscopic resection was performed, and histopathology confirmed ectopic pancreas with local inflammatory changes.In both cases, the resected lesions showed mature pancreatic acini, ducts, and islets, consistent with Heinrich type I and Gaspar-Fuentes type I ectopic pancreas. Case 1 showed no evidence of recurrence by April 2026. Case 2 had no obvious abdominal symptoms during short-term follow-up until April 2026, but long-term recurrence, symptom control, and postoperative complications could not be fully assessed. Conclusion: Ectopic pancreas may present as gastrointestinal wall-based tumor-like lesions and closely mimic GIST or other gastrointestinal subepithelial tumors on preoperative imaging, particularly when typical features such as central umbilication or duct-like structures are absent. Histopathological examination remains essential for definitive diagnosis. Although both patients were biological sisters, the current evidence is insufficient to support hereditary origin or definite familial clustering.