The present invention provides combination therapies useful for treating cancer, particularly breast cancer. The invention provides, in various embodiments, methods of treating a cancer, comprising administering to a patient afflicted therewith of an effective amount an immunoconjugate comprising a monoclonal antibody moiety and a first pro-apoptotic drug moiety linked thereto； and administering to the patient an effective amount of a second pro-apoptotic drug. The monoclonal antibody moiety of the immunoconjugate can act to target receptors of hormone-resistant breast cancer cells, such as HER2. Synergistic effects can be seen when the two pro-apoptotic drugs, acting by a common molecular mechanism (vertical modulation) or different molecular mechanisms (horizontal modulation) are administered to patients afflicted by breast cancer, such as hormone-resistant breast cancer.
