Metastasis is a devastating complication of breast cancer, and tumours over-expressing human epidermal growth factor receptor 2 (HER2) carry higher risk. One strategy to prevent metastasis is to vaccinate against HER2. Although existing HER2 vaccines can induce immune responses, improved clinical outcomes have not yet been demonstrated, and better vaccines are needed. We have developed a new series of vaccines, which uniquely stimulate specific white blood cells to boost immunity against proteins on cancer cells. Phase 1 of this project will establish a model of metastatic breast cancer expressing human HER2 and will test the capacity of a series of HER2-targeted conjugate vaccines to prevent metastasis. In Phase 2, we shall test the ability of these vaccines to elicit anti-HER2 responses within blood immune cells from people with and without breast cancer. Our aim is to develop potent new vaccines with potential to prevent recurrence of HER2 positive breast cancer.