Extraosseous Ewing Sarcoma in a Pelvic Region: A Case Report

Ewing sarcoma is the second most common malignant bone tumour in children. It rarely originates from extraskeletal soft tissue sites such as the upper thigh, buttocks, upper arm and shoulder. Primary extraosseous Ewing sarcoma located in the pelvic region is rare. We report a 17-year-female who had gradual onset of progressive lower abdominal mass and pain. A computed tomography scan revealed well defined lobulated heterogeneously enhancing lesion noted in the pelvic region measuring approximately 12.9 x 9.8 x 9.3 cm. Incisional biopsy showed a small round blue cell tumour which was strongly positive for Cluster of Differentiation 99, vimentin, Friend Leukaemia Integration 1 with 40% Ki-67. Following treatment with chemotherapy, surgery and radiotherapy, there was complete resolution of the tumour. Although extraosseous Ewing sarcoma is rare, it can occur virtually in any soft tissue site. Therefore, clinicians need to distinguish it from soft tissue sarcoma because rapid progression, early diagnosis and timely treatment are crucial for a favourable prognosis.