Thus far, three PARP inhibitors, Olaparib, Rucaparib, and Niraparib, have been approved by FDA for treatment of breast and ovarian cancers in patients with mutations in BRCA1 and BRCA2, which are key mediators of HR repair, providing the first anti-cancer therapy based on synthetic lethality [16,17,18]. The gene discussed is PARP1; the disease is cancer.