Hormone receptor-positive breast cancer, covering luminal A and luminal B subtypes (70–80%) in gene expression profiles, is quite dependent on the hormone receptor pathway, so its mainstream treatment is endocrine therapy with or without targeted agents to interrupt estrogen-signaling pathways and other critical pathways, such as cyclin-dependent kinase (CDK) 4/6 and phosphoinositide 3-kinase (PI3K)-AKT-mechanistic target of rapamycin (mTOR) pathway, for cancer survival. This evidence concerns the gene MTOR and breast cancer.