CASP9 and cancer: Activated PI3K initiates activation of Akt, a downstream kinase of PI3K, which can inhibit apoptosis by protecting caspase cascade through phosphorylation of caspase-9 and promote the expression of anti-apoptotic proteins of the Bcl-2 family proteins, thereby enhancing cell survival and proliferation of cancer cells (Song et al., 2006; Manning and Cantley, 2007).