Epithelioid extragastrointestinal stromal tumor in the pelvic cavity: A rare case at a rare location

Abstract

ABSTRACT Extraintestinal gastrointestinal stromal tumors (EGISTs) are rare stromal tumors involving mesentery, omentum, and retroperitoneum. EGISTs of the pelvic cavity are extremely uncommon, and till date, no case of pure epithelioid type arising from the pelvic cavity has been reported. They pose a diagnostic pitfall as they may mimic ovarian malignancy. We present a unique case of an epithelioid extraintestinal stromal tumor arising from the pelvic cavity. A 43-43-year-old woman presented with complaints of abdominal pain and menstrual irregularities. Ultrasound examination revealed a large well-defined hypoechoic mass in the right pelvic cavity with a possible site of origin from the right ovary. A total hysterectomy with bilateral salpingo-oophorectomy was done. Histopathological examination revealed an encapsulated tumor comprising predominantly of nests and lobules of epithelioid cells with round-to-oval nuclei, vesicular chromatin, and moderate amount of eosinophilic to clear cytoplasm. Mitotic activity was brisk along with focal areas of necrosis. On immunohistochemistry, tumor cells were diffusely and strongly positive for DOG1 and CD117. They were negative for smooth muscle actin, vimentin, S-100, and HMB-45. Based on these findings, a final diagnosis of the high-grade GIST epithelioid variant was made. It is crucial to make the correct preoperative diagnosis of GIST, since these patients may benefit from neoadjuvant imatinib, especially in case of large tumor size.