PIK3CA and breast cancer: In fact, mTOR kinase inhibitors seem to lead to a more effective decrease of PI3K pathway signaling than allosteric mTOR inhibitors given that HER2 amplified breast cancer cells in vitro have been found to be unresponsive to the rapamycin analog (“rapalog”) Everolimus (RAD001; glossary box; Weigelt et al., 2011).