2575 A Rare Case of Extra-Gastrointestinal Stromal Tumor

Abstract

INTRODUCTION: Gastrointestinal stromal tumors (GIST) are tumors of mesenchymal origin rising from the walls of gastrointestinal tract, stomach being most common site followed by small intestine. Those with the similar morphology identified outside the GI tract are termed as Extra-gastrointestinal stromal tumor (EGISTs) and their incidence is about 10%. They are often located in the mesentery, omentum, retro peritoneum, rectovaginal septum, and perivaginal soft tissue and very rarely in prostate. Due to their malignant potential, it is almost essential to diagnose such extra intestinal occurrence. Here, we report a very rare case of EGISTs. CASE DESCRIPTION/METHODS: 61-year-old male with no past medical history presented with intermittent abdominal pain. Physical exam and vital were unremarkable. CT abdomen revealed multilobulated enhancing lesions in mesentery; largest one was approximately 10 × 9 × 8 cm in size. Bowel loops were unremarkable. Diagnostic laparoscopy showed multiple nodules approximately 800 to 1000 in number with size varying from 1 to 10 cm. Diagnosis of EGISTs was made based on immunohistochemistry (IHC). Gross findings: 1st mass: cut surface- creamish white 2nd mass: cut surface- lymph node structure seen Microscopic exam: Histology from 1st mass showed fascicles and solid sheets of round to oval shaped cells and vesicular nuclei with abundant eosinophilic cytoplasm. Mitosis with scanty lymphocytic infiltration and vascular proliferation were also seen. Histology from 2nd mass showed metastasis to lymph nodes. Patient was treated with Imatinib for 10 weeks and largest tumor was removed surgically. Imatinib therapy was continued post surgery as well. DISCUSSION: Due to lack of awareness that GIST can be present in extra intestinal location; they are likely to be misdiagnosed. Pathogenesis and prognosis of EGISTs have not yet been completely understood. Differential diagnosis includes mesothelioma, amelanotic malignant melanoma or metastasis; which can be confirmed out by IHC. (Positive CD117 & CD34 with CK 5/6, pankeratin, desmin, myogenin, s-100 and calretinin being negative in our case). IHC findings favored the diagnosis of EGISTs with metastasis to lymph nodes. As there are specific drugs available for treating EGISTs, it is important to differentiate it from other pathological conditions. This case serves best to promote awareness of GIST in unusual anatomical location and help early diagnosis and prompt subsequent management.