APR exhibited robust Brd4 degradation (with a EC50 = 22 nM), potent cancer cell growth inhibition (IC50 = 56.9 nM in MCF breast cancer cells in vitro), and pronounced antitumor activity in MCF-7 tumor xenografts in vivo (TGI = 77.5%). The gene discussed is BRD4; the disease is neoplasm.