The development of antigen-specific breast cancer vaccines depends on the identification of appropriate target antigens, the establishment of effective immunization strategies, and on strategies to circumvent immune escape mechanisms. Methods such as T cell epitope cloning and serological expression cloning (SEREX) have led to the identification of several target antigens expressed in breast cancer. Some of these target antigens utilized under improved immunization strategies have been shown to induce antigen-specific T cell responses in vivo. In some cases, these were associated with objective clinical responses. Immunoselection of antigen-loss variants was observed in single patients after the induction of strong antigen-specific CD8 + T cell responses in vivo. The challenge is therefore the design of polyvalent vaccination strategies targeting several antigens simultaneously to overcome immune escape in breast cancer. The development of antigen-specific breast cancer vaccines depends on the identification of appropriate target antigens, the establishment of effective immunization strategies, and on strategies to circumvent immune escape mechanisms. Methods such as T cell epitope cloning and serological expression cloning (SEREX) have led to the identification of several target antigens expressed in breast cancer. Some of these target antigens utilized under improved immunization strategies have been shown to induce antigen-specific T cell responses in vivo. In some cases, these were associated with objective clinical responses. Immunoselection of antigen-loss variants was observed in single patients after the induction of strong antigen-specific CD8 + T cell responses in vivo. The challenge is therefore the design of polyvalent vaccination strategies targeting several antigens simultaneously to overcome immune escape in breast cancer.