Phosphoinositide 3-kinase (PI3K) catalyzes the production of phosphatidylinositol-3,4,5-triphosphate by phosphorylating phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2). Growth factors and hormones trigger this phosphorylation event, which in turn coordinates cell growth, cell cycle entry, cell migration, and cell survival. PTEN reverses this process, and research studies have shown that the PI3K signaling pathway is constitutively activated in human cancers that have loss of function of PTEN. PI3Ks are composed of a catalytic subunit (p110) and a regulatory subunit. Various isoforms of the catalytic subunit (p110?, p110?, p110?, and p110?) have been isolated, and the regulatory subunits that associate with p110?, p110?, and p110? are p85? and p85?. In contrast, p110? associates with a p101 regulatory subunit that is unrelated to p85. Furthermore, p110? is activated by ?? subunits of heterotrimeric G proteins.