BETbromodomaininhibitor 1 is an orally active, selective inhibitor of bromodomain and extra-terminal (BET) proteins. It specifically inhibits BRD4 with an IC50 of 2.6 nM. Additionally, BETbromodomaininhibitor 1 demonstrates high affinities towards BRD2(2), BRD3(2), BRD4(1), BRD4(2), and BRDT(2) with Kd values of 1.3 nM, 1.0 nM, 3.0 nM, 1.6 nM, and 2.1 nM, respectively. This compound exhibits anti-cancer activity.