FLI1 and neoplasm: Despite this tight regulation of MYBL2 by EWSR1-FLI1, we noted a marked inter-tumor heterogeneity of MYBL2 mRNA expression in 166 primary EwS (Supplementary Fig. 1e) and in an independent cohort of 208 EwS on protein level stained for p-MYBL2 (Supplementary Fig. 1f).