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 fusion, indicative of Ewing sarcoma. She was thus referred from the gynecologic oncology service to the soft tissue sarcoma service for adjuvant chemotherapy of vincristine/doxorubicin/cyclophosphamide and ifosfamide/etoposide (VDC/IE). We performed a literature review highlighting immunohistochemical and molecular features along with treatment and outcomes in case series of YWHAE-rearranged high-grade endometrial stromal sarcomas and Ewing sarcoma with uterine and/or retroperitoneal involvement.

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.