Growth inhibitory effects of dominant negative FLI1 on Ewing’s sarcoma cell lines support the belief that EWS-FLI1 is involved in EFT development.25 Studies have demonstrated that antisense EWS-FLI1 and EWS-FLI1 siRNA expression in human Ewing’s sarcoma cell lines results in decreased cell growth in vitro and tumorigenicity in in vivo. This evidence concerns the gene EWSR1 and Ewing sarcoma.