The invention features methods to induce and maintain a protective cytotoxic T-lymphocyte response to a peptide of the HER2/neu oncogene, E75, with the effect of inducing and maintaining protective or therapeutic immunity against breast cancer in a patient in clinical remission. The methods comprise administering to the patient an effective amount of a vaccine composition comprising a pharmaceutically acceptable carrier, an adjuvant such as recombinant human GM-CSF, and the E75 peptide at an optimized dose and schedule. The methods further comprise administering an annual or semi-annual booster vaccine dose due to declining E75-specific T cell immunity. The invention also features vaccine compositions for use in the methods.