Phosphatidylinositol 3-kinase (PI3K) plays an important role in the metabolic actions of insulin and is required for adipogenesis. The PI3K pathway has also been identified as an important player in cancer development and progression. The Class IA PI3K heterodimer,which is composed of a P110 catalytic subunit and a P85 regulatory subunit,is activated upon association of the P85 subunit with upstream adaptor proteins or receptor tyrosine kinases. Mutations in PIK3R1 are implicated in cases of breast cancer and associated to SHORT syndrome.