Comparison of 18 F-FDG and 18 F-FAPI PET/CT Findings of Primary Extraskeletal Ewing Sarcoma.

Primary extraskeletal Ewing sarcoma is rare. This report presents a 47‑year‑old man with primary extraskeletal Ewing sarcoma located in the posterior mediastinum, who underwent both 18 F-FDG and 18 F-FAPI-74 PET/CT imaging. The scans demonstrated a notable discordance in tracer uptake: the mass exhibited intense FDG avidity, while FAPI uptake was relatively low and confined to the peripheral rim. The biopsy pathology confirmed the diagnosis of Ewing sarcoma.