PIK3CA and breast cancer: Here we characterise a novel therapeutic ETP-45658 and report the effect following PI3K inhibition on the global gene expression profile in the MCF-7 model breast cancer cell line that contains an oncogenic missense mutation in PIK3CA. The pyrazolopyrimidine derivative ETP-45658 is a potent inhibitor of PI3K that directs the nuclear accumulation of FOXO proteins.