Extraosseous Ewing Sarcoma Presenting as a Shoulder Mass in a 12-Year-Old Girl: A Case Report

Introduction: Extraosseous Ewing sarcoma (EES) is a rare malignant small round cell tumor of soft tissue, and its occurrence in the pediatric shoulder region is particularly uncommon. Case Presentation: We report the case of a 12-year-old girl who presented with a rapidly enlarging subcutaneous mass over the shoulder. The lesion was completely excised, followed by flap reconstruction. Histopathological examination revealed a malignant round cell neoplasm composed of sheets of round to ovoid cells with areas of prominent, staghorn-like vascular pattern. Immunohistochemistry showed strong positivity for CD99 and NKX2.2, supporting a diagnosis of Ewing sarcoma. Although molecular confirmation could not be performed due to resource limitations, integrated diagnostic evaluation incorporating radiologic features and immunohistochemical profile favored an EWSR1–FLI1 fusion-associated Ewing sarcoma.Conclusion: This case highlights the diagnostic challenges in resource-limited settings and underscores the importance of combined histopathological and ancillary techniques for accurate classification. Early recognition, complete surgical excision, and appropriate multimodal therapy are essential for achieving favorable outcomes in this rare presentation.