EWSR1 and Ewing sarcoma: In Ewing sarcoma, the second most common bone cancer affecting children and young adults, the fusion involves EWSR1 and friend leukaemia virus integration 1 gene (EWSR1:FLI1) in nearly 85% of cases, alongside EWSR1:ERG in 10% of cases and rarer fusions with other members of the E-twenty-six (ETS) family of transcription factors).