The invention provides methods for treating triple negative breast cancer (TNBC), by co-administration of a BET bromodomain inhibitor selected from 1-benzyl-6-(3,5-dimethylisoxazol-4-yl)-N-methyl-1H-imidazo[4,5-b]pyridin-2-amine (Compound I), 1-benzyl-6-(3,5-dimethylisoxazol-4-yl)-1H-imidazo[4,5-b]pyridin-2-amine, and pharmaceutically acceptable salts/co-crystals thereof, and a second therapeutic agent to a subject in need thereof. The second therapeutic agent can be a PARP inhibitor, such as, e.g., talazoparib, olaparib or veliparib.