Primary objectives 1. To evaluate the safe ty of administering a HER2 CTL peptide -based vaccine to Stage IV breast and ovarian cancer patients receiving maintenance trastuzumab. 2. To quantify and characterize antigen specific T cell subsets specific to HER2 in PBMC of patients after vaccination wi th a HER2 CTL peptide -based vaccine while receiving maintenance trastuzumab. B. Secondary objectives 1. To evaluate overall survival (OS) in patients who complete a vaccination series with a HER2 CTL peptide - based vaccine while receiving maintenance t rastuzumab. 5. Vaccine Preparation A. HER2 CTL peptide -based vaccine Synthetic peptides will be used. The peptides are 14 -18 amino acids in length with an amino acid sequence identical to the normal HER -2/neu sequence. These peptides have been evaluate d in a previous study (see Background) and are covered by BB IND 6524, Sponsor: Mary L Disis, M.D. The peptides are described below: Table 1. Peptides composing the HER2 CTL vaccine HER2 CTL vaccine peptide Sequence Sequence and location of embedded HLA -A2 binding epitope p369 -384 KIFGSLAFLPESFDGDPA KIFGSLAFL (p369 -377) p688 -703 RRLLQETELVEPLTPS RLLQETELV (p689 -697) p971 -984 ELVSEFSRMARDPQ ELVSEFSRM (p971 -979) B. Peptide synthesis and characterization Peptides are manufactured by Multiple Peptide Systems, San Diego, CA.