Everolimus has been approved to be effective when used with exemestane after progression on non-steroidal aromatase inhibitors in postmenopausal women based on the BOLERO-2 clinical trial. However, the superiority of addition of everolimus to endocrine therapy hasn't been established in the premenopausal women. This is a phase 2, multicentre clinical trial to evaluate the role of everolimus in the first-line endocrine treatment of premenopausal MBC patients after progression on tamoxifen.