Breast cancer ranks second among cancer deaths in women (American Cancer Society, 2005). In the year 2005, the American Cancer Society has estimated that 212,240 new invasive cases of breast cancer will be diagnosed, and predicts 40,410 deaths will result from breast cancer. While 80% of patients present with locoregional disease involving the breast and/or axillary lymph nodes, about half develop disseminated disease and ultimately die from it. Stage IV breast cancer is typically managed with hormonal agents or conventional cytotoxic drugs. Tumors quickly become resistant to these treatments. Immunotherapy is a particularly attractive strategy for overcoming drug resistance and can be integrated with existing therapeutic modalities in an additive or synergistic fashion. Immunotherapy is a type of treatment for cancer based on the idea that the immune system can be activated to destroy cancer cells that might be resistant to hormonal therapy and chemotherapy. A vaccine is a kind of immunotherapy that delivers an antigen (something that activates the immune system) so that the immune system recognizes cells with that antigen as foreign and destroys any cells that display that antigen.