DOG1-Positive Extragastrointestinal Stromal Tumor Presenting As Large Abdomino-Pelvic Mass: A Case Report.

Gastrointestinal stromal tumors (GIST) are mesenchymal tumors commonly arising from the GI tract. Only a small number of GIST originating outside the GI tract have been reported in the literature. They are termed extraintestinal GIST (E-GIST), with histological features similar to GIST. These commonly arise from the omentum, mesentery, or abdominal wall. Microscopic examination shows spindle or epitheloid morphology with immunohistochemistry (IHC) positivity for the cluster of differentiation 117, 34 (CD117, CD34), or discovered on GIST-1 (DOG1). This case series describes the presentation of two cases of E-GIST as an abdominopelvic mass with DOG1 positivity and CD117 negativity on IHC. Patient in the first case presented with a giant abdominopelvic mass, clinically arising from the pelvis with a misdiagnosis of midline desmoid tumor. It was completely excised with a histological surprise of E-GIST with DOG1 positivity on IHC. The second case presented a swelling in the groin region, separate from the testis but arising from the anterior abdominal wall, with histological features of E-GIST with DOG1 positivity. The cases reported here show further evidence regarding the existence of a distinct subset of GISTs characterized by extraintestinal localization, with negative immunohistochemical expression of receptor tyrosine kinases (KIT) and positive DOG1 expression, which appears to be rare and makes DOG1 an emerging marker for GIST.