Vaccines against human breast cancer are an unfulfilled promise. Despite decades of promising preclinical and clinical research, no vaccine is currently available for breast cancer patients. Preclinical research has much to do with this failure, as early mouse models of mammary carcinoma did not mirror the molecular, cellular, antigenic and immunological features of human breast cancer. The advent of HER-2 transgenic mice gave impulse to a new generation of cell and DNA vaccines against mammary carcinoma, that in turn led to the definition of significant antigenic (oncoantigens) and cellular (cancer-initiating cells, preneoplastic lesions, incipient metastases) targets. Future preclinical developments will include the discovery of novel oncoantigens in HER-2-negative mammary carcinoma and the targeting of activated HER-2 molecular variants. Translation to clinically effective vaccines will be fostered not only by new preclinical model systems, but also by the possibility to conduct veterinary vaccination trials in companion animals.