Retroperitoneal Ewing's sarcoma in a woman with advanced breast cancer delineated by contrast‐enhanced ultrasound: A case report

Abstract Extraosseous Ewing's sarcoma is a malignant mesenchymal tumor much rarer than skeletal Ewing's sarcoma. The synchronous or metachronous occurrence of advanced breast cancer with retroperitoneal Ewing's sarcoma is extremely rare. To date, only a few cases of extraosseous Ewing's sarcoma with contrast‐enhanced ultrasound findings have been reported. This study aims to report a case of a retroperitoneal Ewing's sarcoma in a 39‐year‐old woman with advanced breast cancer, where grayscale ultrasound, contrast‐enhanced ultrasound, and computed tomography findings were included. To our knowledge, this is the first reported case of ultrasound and contrast‐enhanced ultrasonography manifestation of retroperitoneal Ewing's sarcoma as a second primary tumor.