Since cancer cells depend on an effective RS response for their survival, considerable effort has been made to develop small-molecule inhibitors of the intra-S checkpoint kinases ATR, CHK1, and WEE1 (Dobbelstein and Sørensen, 2015; Lecona and Fernandez-Capetillo, 2018; Ubhi and Brown, 2019). This evidence concerns the gene ATR and cancer.