ESR1 and breast cancer: Some breast cancers have genetic variation in the oncogenic PI3K/Akt/mTORC1 pathway; therefore, we further stratified the cell lines according to the status of mutations in PI3KCA or PTEN. We found that among ER+ or HER2+ breast cancer cell lines those carrying mutations in PI3KCA or PTEN displayed more apoptosis after RMC-6272 treatment (Fig. 2C).