Emerging PARP inhibitors for treating breast cancer

INTRODUCTION: Some breast cancers harbor defects in DNA repair pathways, including BRCA1 and BRCA2 mutations, leading to a genomic instability. Compromised DNA-damage repair response is found in 11 to 42% of triple negative breast cancers, with a frequency varying according to family history and ethnicity. The oral PARP inhibitors are a promising strategy in breast cancer exploiting Homologous Deficient Recombination deficiency (HRD) by a synthetic lethal approach. Several PARP inhibitors have currently reached early phase trials with studies on going in the adjuvant, neoadjuvant and metastatic setting. Area covered: Here, we review completed and ongoing trials with PARP inhibitors as well as their mechanisms of activity and acquired resistance. Expert opinion: PARP inhibitors show promising results in breast cancer. However, several issues are raised including the identification of biomarkers to predict treatment response and strategies to counteract emerging resistance.