The orally bioavailable bismesylate salt of pictilisib, a small molecule inhibitor of class I phosphatidylinositol 3 kinase (PI3K), with potential antineoplastic activity. Upon administration, pictilisib selectively binds to PI3K in an ATP-competitive manner, inhibiting the production of the secondary messenger phosphatidylinositol-3,4,5-trisphosphate (PIP3) and activation of the PI3K/Akt signaling pathway. This may result in inhibition of tumor cell growth, motility and survival in susceptible tumor cell populations. Activation of the PI3K/Akt signaling pathway is frequently associated with tumorigenesis; dysregulated PI3K/Akt signaling may contribute to tumor resistance to a variety of antineoplastic agents.