PIK3CA and breast cancer: Similarly, in a panel of 18 breast cancer cell lines tested in response to the dual PI3K and mTOR inhibitor BEZ235, it was found that the presence of PIK3CA mutations and HER2 amplification strongly associated with growth inhibition and apoptosis in response to the drug, whereas mutant PTEN cells were seemingly protected and displayed high phosphorylation levels of the mTORC1 target Ribosomal Protein S6 (RPS6) by the ERK pathway [64].