Interleukin-12 may kill tumor cells by stopping blood flow to the tumor and by stimulating a person's white blood cells to kill cancer cells. Monoclonal antibodies such as trastuzumab can locate tumor cells and either kill them or deliver tumor-killing substances to them without harming normal cells. Phase I trial to study the effectiveness of interleukin-12 and trastuzumab in treating patients who have cancer that has high levels of HER2/neu and has not responded to previous therapy