ERG and Ewing sarcoma: In the 15–20% of Ewing sarcomas that are negative for EWSR1–FLI1, variant fusions between EWSR1 (or rarely FUS gene) and other members of the ETS family occur, most commonly ERG (encoding transcriptional regulator ERG) followed by ETV1, ETV4, FEV and E1AF [102,103,104,105].