PIK3CA and breast cancer: The mutation of the PIK3CA gene encoded by phosphatidylinositol3-kinase, PI3K, is the most likely mutated gene in breast cancer mutated genes except HER2 and TP53. About 90% of PIK3CA mutations occurred at H1047R, E545K, and E542K, while mutations at H1047R accounted for about 50% (Yuan et al., 2019).