EIF4EBP1 and small cell lung carcinoma: In examining the differential activation signaling of PI3K/AKT/mTOR in SCLCs, we first determined the phosphorylation levels of AKT(T308), AKT(S473), P70S6K(T389), and 4EBP1(T37/T46) as well as PTEN and PIK3CA in 13 SCLC cell lines (Fig. 1A).