ESR1 and breast cancer: The mTOR signaling pathway plays an essential regulatory role in the development of breast cancer, which is also influenced by other signaling pathways or factors, such as PI3K/AKT, AMPK, ER, HER2, IGF-1R, etc. Furthermore, mTOR inhibitors can inhibit the proliferation, differentiation, and self-renewal of breast cancer stem cells, thus eliminating the root cause of breast cancer.