PIK3CA and breast cancer: In conclusion our data suggest that taking into account PIK3CA CN in addition to mutations might bring to a better evaluation of the PI3K pathway and help elucidating some controversial issues regarding the prognostic and predictive role of PIK3CA. Given the central role of PI3K pathway in tumor biology, outcome and prediction to therapy in patients with HR + /HER2− BC, further studies evaluating the combined effect of PIK3CA gain and mutations are warranted.