MTOR and breast cancer: In advanced-stage breast cancer, combining endocrine therapy with molecular therapies targeting intracellular pathways, such as cyclin-dependent kinase (CDK) 4/6 inhibitors, phosphatidylinositol 3-kinase (PI3K) inhibitors and mammalian target of rapamycin (mTOR) inhibitors, have been highly efficacious when used in combination with endocrine therapy as a backbone [9,10].