Olaparib is in clinical development for the adjuvant treatment of adults who are breast cancer type 1 and type 2 susceptibility protein (BRCA) mutant and human epidermal growth factor receptor 2 (HER2)-negative and have completed local treatment and (neo)-adjuvant chemotherapy. BRCA1 and BRCA2 are proteins that help repair damaged DNA. Adjuvant therapy is additional cancer treatment given after the primary treatment to lower the risk that the cancer will come back. Cancer cells that are HER2 negative may grow more slowly and are less likely to spread to other parts of the body than cancer cells that have a large amount of HER2 on their surface. Olaparib is taken orally and works by blocking a protein called poly [adenosine diphosphateribose] polymerase (PARP). PARP is important to repair damaged DNA. By blocking PARP, the tumour cells may die. If licenced, olaparib will offer a new adjuvant therapy for patients with early BRCA mutated and high-risk HER2-negative breast cancer who have completed local treatment and (neo)-adjuvant chemotherapy.