PIKing the right patient.

HER2 amplification and PIK3CA mutation were validated as biomarkers for sensitivity to the single-agent phosphoinositide 3-kinase (PI3K) inhibitor, GDC-0941, in breast cancer models. A novel expression profile was developed to identify other breast cancers sensitive to PI3K inhibitors. These expression studies highlighted feedback networks connecting TORC1, PI3K, and mitogen-activated protein kinase (MAPK) pathways, and underscored the potential for combination therapies.