PARP1 and cancer: A number of PARP inhibitors have been developed and may be used clinically to treat cancers with homologous recombination (HR) deficiency, such as those with mutations in BRCA1, BRCA2, and PALB2. In these cancers, PARP inhibitors can induce synthetic lethality, and this approach has had some success particularly in breast and ovarian cancer (Janysek et al., 2021).