MTOR and breast carcinoma: In chemotherapy-resistant breast cancer, these pathways further compound other aberrant mechanisms of cell survival, including loss of the PTEN tumor suppressor gene[16], reactivation of phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling[17], expansion of cancer-initiating, progenitor-like cells[18], and increased production of vascular endothelial cell growth factor (VEGF)[19].