Monoclonal antibodies such as trastuzumab can locate tumor cells and either kill them or deliver tumor-killing substances to them without harming normal cells. Interleukin-2 may stimulate a person's white blood cells to kill breast cancer cells. Phase II trial to study the effectiveness of trastuzumab plus interleukin-2 in treating patients who have metastatic breast cancer that has not responded to previous trastuzumab therapy.