MTOR and breast cancer: Abnormal mTOR activity, including the dysregulation of members of its pathway (such as growth factor receptors and tumor suppressors),9 has been documented in several tumor types, including colorectal, lung, and breast cancers.21, 23 Overexpression of growth factor receptors or mutation of their associated receptor tyrosine kinases leads to increased signaling through the PI3K/Akt/mTOR pathway.