Abstract : Sequential endocrine treatments are recommended for estrogen receptor (ER) positive human epidermal growth factor receptor 2 (HER 2) negative metastatic breast cancers except in the case of symptomatic visceral disease. However, patients who suffer from disease progression while receiving a non-steroidal aromatase inhibitor (NSAI) have a very poor prognosis with standard endocrine therapy alone. Recently, based on the results of the BOLERO 2 trial, the mammalian target of rapamycin (mtor) inhibitor everolimus, combined with exemestane, a steroidal aromatase inhibitor, has been approved in Europe and the US for patients suffering from ER positive HER2 negative advanced breast cancer previously treated by a NSAI. The median progression-free survival (PFS) increased from 3.2 to 7.8 months in patients receiving everolimus and exemestane compared to placebo and exemestane. The magnitude of benefit was consistent in all pre-specified subgroups. Side effects were manageable and the quality of life was at least maintained. Everolimus has also been recently studied in HER2 positive locally advanced or metastatic disease in heavily pretreated patients (BOLERO 3 trial). This trial met its primary endpoint. The median PFS was increased in patients receiving trastuzumab, vinorelbine and everolimus compared to patients receiving trastuzumab, vinorelbine and placebo. We review pharmacological data and side effects of the drug. We also review the most important clinical trials leading to reimbursement of everolimus in metastatic breast cancer.