Selectiveinhibition of mTORC1 could be beneficial for treating cancers withaberrant activation of mTORC1 via mutations in the PI3K/mTOR pathway,and indeed, RMC-5552 38 and RMC-6272 40 eachexhibit single-agent antitumor activity in a human xenograft modelof PIK3CA mutant breast cancer in mice in vivo. This evidence concerns the gene PIK3CA and breast cancer.