In this study, we provide inhibitory activity assays and structural and functional studies to demonstrate that 3478 is a potent selective inhibitor of BRD4–BD2 with a novel chemical scaffold and new binding mode to BRD4 bromodomains, and by suppressing c-Myc expression, 3478 reduced the human acute myeloid leukaemia (AML) MV4‐11 cell growth in vitro and xenografted tumour growth in mice without affecting body weight. Here, MYC is linked to neoplasm.