This is a prospective double-blinded, randomized, controlled Phase III clinical trial to determine the effectiveness of Theratope (r) vaccine. Patients entering the trial will have completed first-line chemotherapy for metastatic breast cancer, and have either no evidence of disease or have non- progressive disease. Patients will be stratified upon entry by their status of no evidence of disease or non-progression of disease and by whether the patient will or will not receive concurrent hormonal treatment for their metastatic breast cancer.