PARP1 and cancer: Several PARP inhibitors (PARPi), such as olaparib, rucaparib, and talazoparib, have been approved as targeted chemotherapeutics for the treatment of cancers with mutations in the essential HR genes breast-cancer-associated 1 and 2 (BRCA1 and BRCA2), where the resulting accumulation of DNA DSB leads to genomic instability and eventual cell death [136].