In mice, EWS-FLI expression driven by the Prx1 promoter results in abnormal muscle, cartilage, and bone development, but no tumors (11), while EWS-FLI expression driven from Osterix or Mx1 results in erythroid/myeloid leukemias, but not sarcomas (12, 13). Here, EWSR1 is linked to myeloid leukemia.