Whilst the sensitivity of cells with these imbalances in the DDR to ATR inhibition may not be quite as striking as reported originally for BRCA mutations and PARP, they are similar to our previous determination of sensitivities of HRR-defective human cancer cells to PARP inhibition [39] and other synthetic lethalities with ATM and ATR inhibition [40] and reviewed in [41]). This evidence concerns the gene PARP1 and cancer.