Several factors involved in repair of DSBs were assessed, including BRCA1 (breast cancer 1, early onset), which is a well-known tumour suppressor with critical roles in DNA repair41; 53BP1, which is an important regulator of DSB repair protecting broken DNA ends from processing, a mechanism that is induced by BRCA142,43; and ATM, which is the master regulator of the DNA damage response44. Here, ATM is linked to cancer.