The phosphatidylinositol-3-kinase (PI3K) signaling pathway regulates diverse cellular functions,including cell proliferation, survival, translational regulation of protein synthesis, glucose metabolism, cell migration, and angiogenesis (1). Activating somatic missense mutations of the PIK3CA (phosphatidylinositol-3-kinase catalytic subunit alpha) gene that increase the kinase activity of the PI3Kα protein have been identified in tumor tissues and have been linked to cellular transformation in many different human cancers (2), including hormone receptor positive (HR+) breast cancer (3).