ATR inhibition was previously shown to sensitize cancer cells to various DNA‐damaging agents (Abu‐Sanad et al., 2015; Jossé et al., 2014; Reaper et al., 2011), including synergistic interactions between PARP and ATR inhibition in HR‐deficient tumors (Huntoon et al., 2013; Kim et al., 2017). This evidence concerns the gene PARP1 and cancer.