Many of the anti-cancer drugs currently used for chemotherapy work by causing replication-associated DNA damage that kills individual cancer cells. While this can be an effective way of treating the disease, the drugs often also indiscriminately affect healthy cells, causing unpleasant side effects for the patient. To help resolve this problem, researchers at the Karolinska Institute in Sweden are developing DNA repair inhibitors that are able to selectively introduce toxic DNA damage to cancer cells, while avoiding causing harm to normal cells, to support the successful treatment of cancers and improving patients’ experience of chemotherapy.