EWSR1 and Ewing sarcoma: While there is ample experimental evidence for high EWS-FLI1 levels activating cell cycle- and suppressing differentiation-associated genes, thus driving self-renewal and proliferation of Ewing sarcoma cells, recent studies indicated that low EWS-FLI1 levels may promote Ewing sarcoma migration, invasion and metastasis [122,202,203].