CF53 is a highly potent, selective and orally active inhibitor of BET protein, with a Ki of <1 nM, Kd of 2.2 nM and an IC50 of 2 nM for BRD4 BD1. CF53 binds to both the BD1 and BD2 domains of BRD2, BRD3, BRD4, and BRDT BET proteins with high affinities, very selective over non-BET bromodomain-containing proteins. CF53 shows potent anti-tumor activity both in vitro and in vivo.