Integrating PARP inhibitors into the management of breast cancer: where are we?

During the last 2 decades, extensive research has focused on the molecular functions of BRCA1 and BRCA2 genes. This has led to the development of Poly(ADP-ribose) polymerase inhibitors (PARPi), as effective target therapies, based on their preferential cytotoxicity in tumor cells harboring germline BRCA1 and BRCA2 mutations. At the present time, 2 PARPi (Olaparib and Talazoparib) are approved as single agent for the treatment of patients with metastatic HER2-ve breast cancer, who have BRCA germline mutations. The clinical benefit of these agents might be also anticipated in patients harboring germline mutations in some additional genes involved in the process of homologous recombination repair (HRR) other than BRCA1/BRCA2. In this review, we summarize the molecular rational for the therapeutic development of PARPi and the clinical evidence supporting their use as anticancer drugs in breast cancer patients with BRCA1/BRCA2 germline mutations. We also discuss the role of platinum-based chemotherapy and how it compares with PARPi in the management of these patients. We will go through some relevant clinical trials of various combinations of PARPi with cytotoxic or immunotherapeutic agents, which may potentially provide better treatment results, compared to what is already achieved with their use as monotherapy.