Ewing Sarcoma Displaying Extensive Well Differentiated Neuroblastomatous Differentiation: A Case Report

Introduction A tumor with EWSR1/FLI fusion displaying extensive well differentiated neuroblastomatous differentiation is presented. Case report A nine-year-old female patient had a thoracic vertebra 8 paraspinal mass. The lesion was resected incompletely. Histopathologically, a small round cell tumor with gangliomatous differentiation was seen. This was initially diagnosed as an intermixed ganglioneuroblastoma. In the completion surgery biopsy material, the small round cell component was more prominent. Immunohistochemistry for both samples showed membrane positivity for CD99 and nuclear positivity for NKX2.2 in the small round cell component of the tumor. Molecular analysis revealed EWSR1/FLI fusion. The diagnosis then considered a "Ewing Sarcoma Displaying Extensive Well Differentiated Neuroblastomatous Differentiation". Conclusion Tumors with the EWSR1/FLI fusion may show neuroblastomatous differentiation. We chose to treat this as an Ewing Sarcoma (ES). Recognition of this phenomenon in ES cases may prevent a possible misinterpretation and a failure in oncologic treatment