Supplementary Material for: Rare Extraskeletal Ewing Sarcoma of the Anterior Abdominal Wall: A Diagnostic Challenge

Ewing sarcoma (ES) is a highly malignant neoplasm, typically arising from bone in children and young adults. Extraskeletal Ewing sarcoma (EES), involving soft tissues without bone involvement, represents a small fraction of ES cases. Even rarer is its manifestation in the anterior abdominal wall. We report a case of a 27-year-old male presenting with right iliac fossa pain and a palpable mass, ultimately diagnosed as EES of the anterior abdominal wall. Radiological imaging revealed a soft tissue tumour within the rectus sheath with evidence of pulmonary metastasis. Histopathological analysis revealed small round blue cells, and immunohistochemistry demonstrated strong positivity for CD99, FLI1, WT1, and synaptophysin, confirming the diagnosis. Treatment was initiated with multi-agent chemotherapy and radiotherapy, and the patient remains under ongoing follow-up. This case underscores the diagnostic challenge EES poses in atypical locations, requiring a high index of suspicion and a multimodal diagnostic and therapeutic approach.