How to overcome endocrine resistance in early and metastatic breast cancer

According to St. Gallen Consensus, endocrine responsive breast cancer is defined by positive steroidal receptors (ER= estrogen receptor and PR= Progesterone Receptor). ER/PR and HER2 are the most important biomarkers in decisionmaking about adjuvant and palliative treatment options. Available data suggest, that the higher the expression of ER and PR, the better the outcome for patients with early and advanced breast cancers. In early breast cancer setting, there is a high risk of recurrence for patients with luminal types, even after 5 years of treatment with aromatase inhibitors. Therefore several strategies to improve outcome in these patients are applied today, e.g.: 1) extended endocrine therapy, 2) CDK4/6 inhibitors, 3) mT or inhibitors or 4) bone modifying agents like bisphosphonates. In this review, we focus on endocrine therapy resistance in early and late stage breast cancer, including resistance's prevention, endocrine treatment and responsiveness in early and advanced breast cancer. Major Phase II/III studies for CDK4/6 and PI3CA inhibitors in the metastatic setting are discussed. Finally, strategies to prevent patients with early breast cancer from recurrence are presented.