FLI1 and neoplasm: These results suggested either (i) the single hit of EWS-FLI1 expression in a subset of cells was not sufficient to induce tumor formation in the mouse (e.g. EWS-FLI1 might not have been expressed in enough cells to facilitate tumorigenesis) or (ii) the Ews-Fli1 translocation event never occurred in the first place.