Specific ATR inhibitors (ATRi), such as VE-821 and AZD6738, sensitize diverse cancer cell models to genotoxic agents, including cross-linking agents, topoisomerase I or II inhibitors, PARP inhibitors and the nucleoside analog gemcitabine [173–177], by allowing premature mitosis with incomplete DNA replication or chromosome separation. Here, ATR is linked to cancer.