Accordingly, molecular targeting drugs have been developed, such as mechanistic target of rapamycin (mTOR) or cyclin-dependent kinase (CDK) 4/6 inhibitors, thus diversifying the treatment strategies for patients with relapsed or metastatic ER-positive BC (Goetz et al. 2017; O'Leary et al. 2016; Baselga et al. 2012; Hortobagyi et al. 2016). This evidence concerns the gene MTOR and breast cancer.