EWSR1 and Ewing sarcoma: GDF6 emerged as such dependency created by EWS-FLI1: GDF6 is a direct transcriptional activation target of EWS-FLI1 and is highly expressed in Ewing sarcoma (Figure 1), and silencing of GDF6 profoundly impaired in vitro and in vivo growth of Ewing sarcoma (Figure 2).