PIK3CA and breast cancer: To confirm the role of signalling molecules in predicting response to agents targeting the PI3K/AKT/mTOR pathway, we next compared the sensitivity to capivasertib in two HR+/HER2- breast cancer cell lines, namely T47D and MCF-7, harbouring hotspot mutations of PIK3CA (H1047R and E545K, respectively) [38] with diverse levels of activation of the PI3K/AKT/mTOR axis (Fig. 4e).