TCF3 and acute lymphoblastic leukemia: Idelalisib has been shown to have a number of effects on ALL, including down-regulating the PI3K-AKT-mTOR pathway and decreasing leukemia burden in a mouse model of Philadelphia(Ph)-like ALL [12], decreasing growth and cell cycle progression in pre-B ALL cell lines (but not the pro-B or mature B ALL cell lines tested) [13], and inducing apoptosis in a patient sample of relapsed ALL with a TCF3-PBX1 fusion [14].