EWSR1 and Ewing sarcoma: Although EWSR1::FLI1 induces growth arrest or apoptosis in differentiated primary cells (11, 12), its expression in human mesenchymal stem cells (hMSC) recapitulates the Ewing sarcoma gene signature, with stronger induction of oncogenic targets in human pediatric MSC (hpMSC; refs. 9, 13).