Certain ductal carcinoma in situ (DCIS) lesions overexpress the HER-2/neu receptor at this early stage of breast cancer development. Recently, we showed that a HER-2-targeted dendritic cell vaccine could be used to eliminate HER-2-overexpressing cells in patients that harbor these high-risk DCIS lesions. Our findings suggest that vaccinating such patients might diminish the risk of recurrence, protect against the development of invasive breast cancer, and minimize morbidity associated with current treatments. We discuss several implications of this work for developing effective cancer vaccines.