The utility of ATR pathway inhibitors combined with RNRi for the treatment of ES is also supported by reports on the cooperative action of inhibitors of the ATR downstream effector kinases CHEK1 and WEE1 with RNRi in ES (Goss et al. 2017; Koppenhafer et al. 2018; Ohmura et al. 2021). Here, CHEK1 is linked to Ewing sarcoma.