PIK3CA and breast cancer: In the pivotal phase III randomized trial SOLAR-1 that confirmed the predictive value of PIK3CA-mutation status on the clinical benefit of the PI3K-α-selective inhibitor alpelisib in PIK3CA-mutated patients with HR + /HER2- advanced or metastatic BC [8, 9, 38], the vast majority of PIK3CA mutations were determined at the primary tumor (77%) rather than at the metastatic sites (22%) [39], whereas no matched tumors have been evaluated.