The purpose of this study is to examine the immunological response rate to administration of the THERATOPE® vaccine in women with stable metastatic breast cancer who are being treated with aromatase inhibitors or Faslodex® and who do not require chemotherapy. Post-menopausal women on aromatase inhibitors or Faslodex® alone and pre-menopausal women on aromatase inhibitors plus luteinising hormone-releasing hormone (LH/RH)-agonist may be eligible to be enrolled. Patients must not have had radiotherapy or major surgery within four (4) weeks prior to entering the study. Information about the safety and tolerability of administration of the THERATOPE® vaccine will also be gathered during the course of the study.