3022 Background: The phosphatidylinositol 3-kinase (PI3K) pathway is a promising target in cancer. CH5132799 is a novel PI3K inhibitor, selectively inhibiting class I PI3Ks (α, β, δ and γ) with no inhibition of class II and III or mTOR, and with potent antitumor activity in preclinical studies (Tanaka et al, Clin Cancer Res; 17; 3272-81, 2011). First-in-human study objectives were determination of maximum tolerated dose (MTD), safety/tolerability, PK/PD and clinical activity (RECIST). Methods: A 3+3 dose escalation design was used. The initial dosing schedule of CH5132799(schedule A) was once a day (QD). Due to a relatively short half-life, a twice a day (BID) schedule (schedule B) was introduced. PK profiles were studied over 72 hours. PD analyses included quantification of various phosphoproteins in platelet rich plasma (PRP). Tumor assessments were performed at baseline and cycle 3 day 1 (C3D1) and FDG-PET scans at baseline, C1D8 and C3D1. Results: 29 patients (pts) with a variety of solid tumors have ...