For example, PARP1/2 inhibitors (PARPi), which block PARP1/2 mediated poly-ADP-ribosylation (PARylation) and trap PARP1/2 on DNA, have been used in around 10–20% of patients with breast, ovarian and other cancers with BRCA1/2 mutations or homologous recombination (HR) deficiency (HRD)25–27. The gene discussed is BRCA1; the disease is cancer.