The combination of mTOR inhibitors with endocrine agents has been incorporated into clinical practice after the publication of the BOLERO 2 trial, a randomized phase III study that demonstrated significant improvement in PFS with the addition of the mTOR inhibitor everolimus to the steroidal AI exemestane (39) in patients with HR+ advanced breast cancer that progressed after non-steroidal AI therapy. This evidence concerns the gene MTOR and breast cancer.