In breast cancer, mutations of the PIK3CA gene, which encodes thep110α catalytic subunit of PI3K, are highly frequent(2,257/9,095 = 24.82% according to the Catalogue of somatic mutations incancer [2]), have been shown to be oncogenic, and are likely to represent importantevents in the initiation and progression of breast cancer. This evidence concerns the gene PIK3CA and breast cancer.