EWSR1 and Ewing sarcoma: The DNA damage response protein, poly(ADP-ribose) polymerase 1 (PARP1), was identified as a potential target in Ewing sarcoma following demonstration that PARP1 is a transcriptional coregulator of EWS-FLI1 [34] and that the translocation is a genetic determinant of PARP sensitivity in cellular models.