Preclinical and clinical studies identified in PubMed (searching for “cancer”, “PARP”, and “BRCA” or “DNA repair” between Jan 1, 2005 and July 1, 2019, with no language restrictions) have established a correlation between different DNA repair defects and sensitivity to PARP inhibition in different tumour types, leading to drug approvals in ovarian and breast cancer. The gene discussed is PARP1; the disease is cancer.