A giant gastrointestinal stromal tumor of the stomach presenting as a posterior mediastinal mass.

Gastrointestinal stromal tumors (GISTs) involving thoracic region are very rare, most of which are esophageal in origin. Herein, we report a gastric GIST presenting as a posterior mediastinal mass, which provided diagnostic pitfalls due to its unusual anatomic location. The patient was a 68-year-old Chinese female, presenting with dysphagia, nausea and weight loss of 5 kg within 4 months. The contrast-enhanced thoracic computed tomography scan revealed a huge heterogeneous soft tissue mass in the posterior mediastinum. The core biopsy revealed a spindle cell tumor. The pathological features, in conjunction with the strong immunostaining pattern for CD117 and DOG-1 and the identification of exon 11 mutation, confirmed the diagnosis of GIST. The subsequent surgery revealed the tumor located entirely in the abdominal cavity, laying beneath the diaphragm, and pushing the diaphragm upward into the posterior mediastinum. To our best, there has been only one similar case reported in the English literature. As patients with GISTs either resectable or not may get potential benefits from imatinib currently, the identification of GIST is very important even before surgery. Clinicians and pathologists should keep in mind that GISTs involving thoracic region do exist. The morphological features, immunohistochemical panel including CD117 and DOG-1 and molecular genetic test, in combination with clinicopathological correlation are helpful in confirming the correct diagnosis.