Axial Round Cell Sarcoma Harboring a Non-ETS EWSR1 Rearrangement: Diagnostic Challenges and Clinical Implications.

We present a rare case of a cervicothoracic epidural spindle and round cell sarcoma in a 59-year-old man, characterized by an EWSR1 gene rearrangement. The patient experienced progressive cervical pain and lower limb weakness due to an extradural mass at the C7-T2 level. Surgical resection and cervicothoracic fixation were performed, followed by radiotherapy (30 Gy/10 fractions) and Ewing-based chemotherapy (doxorubicin/ifosfamide). Histopathological analysis revealed a spindle and oval cell neoplasm with a Ki-67 index of 30%. The tumor was positive for CD99, SATB2, TLE1, cyclin D1, and focal FLI1, while negative for EMA, S100, desmin, calponin, and SOX10. Fluorescence in situ hybridization (FISH) analysis confirmed EWSR1 break-apart signals (3-8) in 70% of nuclei and separation in 18% of cells, indicating an EWSR1-non-ETS fusion. Local recurrence occurred despite multimodal therapy. This case highlights the clinical and diagnostic challenges associated with EWSR1-rearranged non-ETS sarcomas, which exhibit distinct molecular behaviors, morphology, and treatment responses compared to classical Ewing sarcoma.