However, several issues have complicated PIK3CA mutations as a predictive biomarker in BC: (i) PIK3CA mutations have been associated with a relatively better prognosis compared with PIK3CA wild-type BC patients [7], [9], (ii) the mutations are not associated with higher proliferation indices or lower efficacy with hormonal therapy which would be hypothesized from oncogenic activation of PIK3CA[8], and (iii) PIK3CA mutant breast cell lines have been associated with sensitivity to tamoxifen [7], [20]. This evidence concerns the gene PIK3CA and breast cancer.