Endocrine Abstracts

Extra-gastrointestinal stromal tumors (EGISTs) in the retroperitomeum are extremely rare. A 44-year-old man was referred from a private clinic suspicious of an adrenal tumor that was incidentally detected by abdominal ultrasound. Computed tomography (CT) scan showed a retroperitoneal mass of 12 cm harboring a feeding artery from the left adrenal gland contiguous with the left adrenal gland, which enhanced heterogeneously on post-contrast imaging. By magnetic resonance imaging, the tumor demonstrated heterogeneous low intensity in T₁ weighted images and an extremely heterogeneous lesion composed of high and low signal intensity in T₂ weighted images. PET CT imaging with fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) demonstrated ¹⁸F-FDG accumulation in the tumor in the early and late phase. Iodine-123-metaiodobenzylguanidine and iodine-131-adosterol scintigram did not detect any accumulation in the tumor. The results of all conducted serum and urinary examinations of adrenocortical hormone and catecholamine were within the normal range. Adrenalectomy was performed. Histopathological diagnosis of the tumor was GIST. Immunohistochemical findings revealed that the neoplastic cells were positive for c-kit and CD34 and negative for S100 protein, alpha-SMA, and desmin. Mitotic activity (2–3/50 high power field) and the labeling index for MIB-1 (about 3.2%) were low. The GIST was diagnosed as a high-risk tumor because its diameter was over 5 cm. We started imatinib 400 mg/day according to the Japan GIST guideline 1 month after operation.