PARP inhibitors inactivate the PARP family of enzymes and are approved for use in the treatment of metastatic germline BRCA1 or BRCA2-mutated breast cancers and in the adjuvant setting for high-risk, HER2-negative germline BRCA1 or BRCA2-mutated early breast cancer [116,117,118]. This evidence concerns the gene ERBB2 and breast cancer.