FLI1 and Ewing sarcoma: Ewing sarcoma (ES) is the second most common bone or soft-tissue tumor affecting children, adolescents, and young adults; is characterized by pathognomonic FET/ETS gene fusions (85% of cases are EWSR1/FLI1); and is an invasive tumor with characters of early metastatic spread, high recurrence, and low 5-year survival [1–3].