Address for correspondence

Endometrial stromal sarcoma (ESS) is a mesenchymal neoplasm that usually occurs as a primary tumor of the uterine corpus, but rarely arises in other sites, such as the ovary, pelvic cavity, mesentery, omentum and intestine. Herein, we present a rare case of low-grade ESS presented as prevesical mass. A 60-yr-old woman who had undergone total hysterectomy for endometriosis eleven years ago was presented with incidentally detected prevesical pelvic mass. Since malignant transformation of urachal remnants was possible, the mass was suspected to be a urachal tumor. Extraction of the mass was performed, and the histopathologic diagnosis was lowgrade ESS. In summary, prevesical tumor is rare but in patients with endometriosis, we suggest endometriosis and its possible malignant changes should be taken into account in the differential diagnosis of prevesical mass.