Extraskeletal Ewing sarcoma in the anterior abdominal wall

Introduction. Extraskeletal Ewing sarcoma (ES), is highly malignant neoplasm occurring most commonly in the thoracic wall and paravertebral region. ES belongs to the group of small round cell tumors and displays pathognomonic structural abnormalities of EWS gene. The aims of this article was to present extraskeletal ES in extremely rare anatomic location, an unusual clinical presentation, and modified treatment strategy. Case outline. A 15-year-old boy was admitted to the hospital with acute abdominal pain in the right iliac region. During urgent operation, because of suspected appendicitis with periappendicular infiltrate, partly haemorrhagic tumor tissue was discovered in the preperitoneal space. Histopathological and immunohistochemical analyses revealed tumor resembling extraskeletal ES. Postoperative CT scan has shown the tumor rest, which was completely removed in the second operation. The molecular genetic analysis confirmed extraskeletal ES by finding of the EWSR1-FLI1 fusion gene. Chemotherapy and radiotherapy according to VAC protocol were started, and the patient is free of the disease eight months after the first operation. Conclusion. Our case is the fourth case of extraskeletal ES located in the abdominal wall, the second case confirmed by molecular genetic finding, and the first case described in children at this anatomic location. Due to extremely rare location, unusual clinical presentation, and needed genetic analysis, the strategy of tumor treatment was modified with the good short-term result.