PI3K (Phosphatidylinositol-4,5-bisphosphate 3-kinase) is a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which in turn are involved in cancer. Many of these functions relate to the ability of class I PI 3-kinases to activate protein kinase B (PKB, aka Akt) as in the PI3K/AKT/mTOR pathway. The p110δ and p110γ isoforms regulate different aspects of immune responses. PI 3-kinases are also a key component of the insulin signaling pathway. The pathway, with oncogene PIK3CA and tumor suppressor PTEN, is implicated in insensitivity of cancer tumors to insulin and IGF1, and in calorie restriction. PI3K family is divided into four different classes: Class I, Class II, Class III, and Class IV. The classifications are based on primary structure, regulation, and in vitro lipid substrate specificity.