An Unusual Case of Cutaneous Ewing Sarcoma of the Anterior Abdominal Wall in an Adult Patient.

Ewing sarcoma is a malignant small round blue cell tumor most commonly found in the bones of children and adolescents. Cutaneous Ewing sarcoma, originating in the skin and subcutaneous tissues, is exceedingly rare, especially in adults. We present the case of a 57-year-old woman who developed a progressively enlarging mass on her anterior abdominal wall. The lesion grew over several months and became increasingly erythematous. The mass was initially misdiagnosed as a soft tissue infection and the patient was treated with antibiotics followed by attempted incision and drainage with no clinical resolution. Imaging studies, including a contrast-enhanced CT scan, revealed a lobulated heterogeneous soft tissue mass measuring 5 x 3.9 x 5.2 cm, abutting and possibly infiltrating the left rectus muscle. The patient subsequently underwent radical resection with close but negative margins. Histopathological examination demonstrated small round blue cells arranged in solid sheets with associated vasculature. Immunohistochemical staining was positive for GATA3 and showed CD56 positivity, while negative for multiple other markers, aiding in excluding alternative diagnoses. Molecular studies confirmed the diagnosis of Ewing sarcoma. Postoperative management involved a multidisciplinary approach, including plans for systemic chemotherapy and consideration of adjuvant radiation therapy due to the high risk of local recurrence in the setting of close margins. Cutaneous Ewing sarcoma typically presents as a rapidly enlarging mass that may resemble benign conditions such as sebaceous cysts or inflammatory processes. The key to its identification is histopathological evaluation, including immunohistochemical staining, as well as molecular testing to detect characteristic genetic translocations like the EWSR1-FLI1 fusion gene. Early and accurate diagnosis is crucial due to the tumor's aggressive nature and high potential for metastasis. Implementing a multidisciplinary treatment plan encompassing surgery, chemotherapy, and possibly radiation therapy is essential for improving patient outcomes.