In spite of the demonstrated coexistence of tumor-associated rejection antigens expressed by breast tumors along with T cells that are capable of recognize them, breast cancers arises in immunocompetent hosts, outmaneuver immune recognition and ultimately progress to widely disseminated disease. In recent years, several explanations have been proposed to account for the inability of the immune system to recognize and reject antigenic breast tumors. Among them, the immune tolerance mechanisms have gained particular attention. Here, we discuss the increasing evidence pointing to tolerance towards tumor antigens as an important explanation for the failure of the immune system to reject breast tumors. A better understanding of the cellular and molecular mechanisms involved in breast tumor-induced antigen-specific T-cell tolerance may lead to approaches to effectively harness the immune system against this malignancy.