Multiple clinical trials carried out since 2009 have demonstrated PARP inhibitor efficacy in BRCA mutated ovarian and breast cancer, but also prostate, pancreatic cancer, and small cell lung carcinoma (SCLC), irrespective of the BRCA status (Weaver and Yang 2013; Sonnenblick et al. 2015; Mirza et al. 2018; Franzese et al. 2019; Keung et al. 2019; Mateo et al. 2019; Pant et al. 2019; Pilie et al. 2019a). Here, PARP1 is linked to breast cancer.