Based on previous reports showing that chimeric transcription factors, such as EWS-FLI1 in Ewing sarcoma, can themselves render cells sensitive to ATR inhibition through induction of replication stress30,31, we hypothesized that PAX3-FOXO1 may contribute to replication stress and sensitivity to ATR inhibition in ARMS. This evidence concerns the gene PAX3 and Ewing sarcoma.