PARP1 and cancer: A new therapeutic strategy, synthetic lethality (SL), has recently been introduced for cancer subtype–specific chemotherapy, and this was first exemplified by the treatment of homologous recombination defect (HRD) breast cancers carrying BRCA1/2 mutations (BRCAness) with PARP inhibitors (PARPis), including olaparib and talazoparib (14).