PARP1 and breast cancer: Poly(ADP-ribose) polymerase 1 (PARP-1) is able to detect radiation-induced DNA SSBs, and then recruit DNA repair proteins to facilitate DNA repair.1 Following radiation, inhibition of PARP-1 inhibits SSB DNA repair, which can inhibit DNA synthesis leading to collapsed replication forks, increased DNA double-strand breaks and the subsequent cell death.2 PARP inhibition has been shown to enhance the effects of radiotherapy in various pre-clinical tumour models including lung cancer,3–6 breast cancer,4 prostate cancer and colon cancer.7