An update on PARP inhibitors—moving to the adjuvant setting

Inhibition of poly(ADP-ribose) polymerase (PARP) enzymes is a potential synthetic lethal therapeutic strategy in cancers harbouring specific DNA-repair defects, including those arising in carriers of BRCA1 or BRCA2 mutations. Since the development of first-generation PARP inhibitors more than a decade ago, numerous clinical trials have been performed to validate their safety and efficacy, bringing us to the stage at which adjuvant therapy with PARP inhibitors is now being considered as a viable treatment option for patients with breast cancer. Nevertheless, the available data do not provide clear proof that these drugs are efficacious in the setting of metastatic disease. Advancement of a therapy to the neoadjuvant and adjuvant settings without such evidence is exceptional, but seems reasonable in the case of PARP inhibitors because the target population that might benefit from this class of drugs is small and well defined. This Review describes the evolution of PARP inhibitors from bench to bedside, and provides an up-to-date description of the key published or otherwise reported clinical trials of these agents. The specific considerations and challenges that might be encountered when implementing these compounds in the adjuvant treatment of breast cancer in the clinic are also highlighted.