FLI1 and Ewing sarcoma: With this in mind, we looked for transcriptional regulators that were positively or negatively regulated by EWSR1-FLI1 in the Ewing sarcoma cell line A673 using the well-established cell model A673/TR/shEF in which EWSR1-FLI1 is downregulated by a specific doxycycline-dependent shRNA [19].