PARP1 and breast cancer: Further clinical trials are aimed at extending the use of these drugs to breast cancer, prostate cancer and pancreatic cancer, to test further PARP inhibitor compounds, and to define patient pools that benefit from PARP inhibitor treatment in the absence of BRCA1/2 germline mutations.4–6 The use of PARP inhibitors in a maintenance or adjuvant setting mandates a careful assessment of any late-onset side effects.