Loss of 53BP1 Causes PARP Inhibitor Resistance in <i>Brca1</i> -Mutated Mouse Mammary Tumors

In this study, we show that loss of 53BP1 causes resistance to PARP inhibition in mouse mammary tumors that are deficient in BRCA1. We hypothesize that low expression or absence of 53BP1 also reduces the response of patients with BRCA1-deficient tumors to PARP inhibitors.