Undifferentiated small round cell sarcoma of the parapharyngeal space in a 4.5-year-old patient:A rare case report.

This case report describes a 4.5-year-old girl diagnosed with a rare Undifferentiated Small Round Cell Sarcoma (USRCS) originating in the parapharyngeal space with multiple lung metastases. Diagnostic workups, including imaging, immunohistochemistry, and genetic sequencing, identified the tumor as an unclassified subtype of USRCS. The patient was treated with the Ewing sarcoma chemotherapy regimen, alternating between VDC (vincristine + doxorubicin + cyclophosphamide) and IE (ifosfamide + etoposide), in combination with bevacizumab. The tumor achieved complete remission, and no recurrence has been observed during follow-up.