Although coexistent mutations of AKT1 and PIK3CA mutations are suggested to be infrequent in breast cancer (Carpten et al, 2007; Bleeker et al, 2008), it remains to be elucidated whether AKT1 mutations are mutually exclusive with all the other PI3K–AKT-activating alterations in various tumour types. This evidence concerns the gene PIK3CA and breast cancer.