A phosphoinositide 3-kinase inhibitor (PI3K inhibitor) is a class of medical drug that functions by inhibiting one or more of the phosphoinositide 3-kinase enzymes, which are part of the PI3K/AKT/mTOR pathway, an important signalling pathway for many cellular functions such as growth control, metabolism and translation initiation. Within this pathway there are many components, inhibition of which may result in tumor suppression. These anti-cancer drugs are examples of targeted therapy. They are being actively investigated for treatment of various cancers, both alone and in combination.