By normalizing to a line that did not express mouse Ews-Fli1 and using a positive control for mouse Ews-Fli1 expression (mouse EWS-FLI1-overexpressing MEFs), we demonstrated that none of the tumors from the Ink4a/Arf tumor study expressed Ews-Fli1 at levels above background (Supplementary Figure S21B). This evidence concerns the gene EWSR1 and neoplasm.