In developed countries, cancer has replaced infectious diseases as a major cause of death. Currently, efforts in the immunoprevention of cancer are beginning to resemble that presented by the prevention of infectious diseases by immunization a century ago. Breast cancer is the most frequent type of tumor in women and is the first cause of death by this illness, among them. Moreover, cancer incidence will grow during next years. Some findings in autoimmunity related to breast cancer in animal models have been important to clarify mechanisms that potentiate tumor growth. Clinical and experimental data now clearly indicate that chronic inflammation significantly contributes to cancer development. Emerging out of these studies is an appreciation that persistent humoral immune responses exacerbate recruitment and activation of innate immune cells in neoplastic microenvironment where they regulate tissue remodeling, pro-angiogenic and pro-survival pathways that together potentiate cancer development. Generally, antigens involved in autoimmune response in breast cancer are modified self-proteins or over-expressed normal proteins that induce autoantibodies (autoAbs) formation which exhibit tumor promoting actions. This article will review recent results concerning to the ability of muscarinic acetylcholine receptors (mAChR) expressed in transformed cells, to trigger auto- Abs formation either in experimental models or in breast cancer patients. We will also discuss the action of these antibodies as agonists in mAChR functions.