Extraskeletal Ewing sarcoma with uterine cornua attachment mimicking high grade endometrial stromal sarcoma: A case report and brief literature review.

Background: Ewing sarcoma is an EWSR1-rearranged aggressive malignancy that occurs commonly in bone and has small round blue cell morphology. A diagnostic challenge is presented in the cases of extraskeletal Ewing sarcoma involving solid organs, such as the uterus. Case report and brief literature review: We present the case of a 54-year-old female with a large pelvic mass connected to the uterine cornua and retroperitoneal soft tissue. Upon surgical debulking, the mass was characterized by infiltrative tumor cells with high nuclei-to-cytoplasmic ratio invading from the serosal surface into the myometrium. The initial diagnostic work-up was muddied by radiographic suggestion of uterine origin, histologic identification of uterine involvement and diffuse positivity for Cyclin D1, KIT and CD99, which raised the diagnostic possibility of high-grade endometrial stromal sarcoma. However, molecular testing that revealed Conclusion: This case and accompanying literature review highlight the benefit of molecular testing in the context of round cell tumors involving the uterus and the importance of distinguishing high-grade uterine stromal sarcomas from sarcomas of soft tissue origin, as they have different treatment strategies.