The selective PI3Kα inhibitor BYL719 has shown preferential sensitivity in PIK3CA-mutated cell lines, and a first-in-man study with this agent (NCT01387321) is enrolling patients with PIK3CA mutation or amplification only to maximize the potential benefit of treatment.9 Preliminary results from this phase I trial of single-agent BYL719 in patients with advanced solid tumors suggests a favorable safety profile, with two confirmed partial responses observed (one each in patients with HR-positive breast cancer and cervical cancer).9 This evidence concerns the gene PIK3CA and breast cancer.