The observation that BRCA-mutated breast cancers show an impairment in HR pathways [19], and that some sporadic TNBC are phenocopies of BRCA1-mutated cancers (i.e. they display a phenotype resembling BRCA1-mutated cancers without harboring a BRCA1 mutation, a feature also defined as “BRCAness”, see below) [20, 21], led to exploration of the application of PARP inhibition to the treatment of breast cancer (BRCA-associated and TNBC). Here, PARP1 is linked to breast cancer.