Fine-needle aspiration cytology for the diagnosis of ewing's sarcoma in bone: a case report

Ewing's sarcoma (ES) is an aggressive small round cell tumor traditionally diagnosed through open biopsy. We present a systematically evaluated case suggesting that standardized ultrasound-guided fine-needle aspiration cytology (FNAC), when combined with immunohistochemical (IHC) and molecular analysis, may provide diagnostic reliability approaching that of open biopsy. A 26-year-old female presented with an insidiously developing left popliteal fossa mass. Ultrasound-guided FNAC demonstrated characteristic small round blue cells, with IHC showing diffuse positivity for CD99, FLI-1, and Bcl-2. Subsequent fluorescence in situ hybridization (FISH) analysis identified the EWSR1 gene rearrangement. The patient exhibited significant radiographic response to neoadjuvant chemotherapy after two cycles, as evidenced by MRI. Definitive surgical resection specimens similarly demonstrated EWSR1 rearrangement by FISH, corroborating the initial diagnosis. Following four adjuvant chemotherapy cycles, the patient achieved disease-free status at the last follow-up. This case highlights the potential utility of optimized FNAC specimen triage (incorporating smears, liquid-based cytology, and cell blocks) for rare tumors, enabling comprehensive ancillary testing while maintaining diagnostic accuracy and supporting timely therapeutic decision-making.