The vaccine is injected under the skin and then moves into the site of vaccine injection to attract attention from the immune cells called dendritic cells. It is dendritic cells that send hazardous signals that stimulate an immune response. Typically, when dendritic cells encounter tumor cells, they won’t awaken the immune system because the tumor cells are not recognized as foreign. In effect, however, the breast cancer vaccine shows dendritic cells that tumor cells differ from normal cells and must therefore be attacked and destroyed. The use of the vaccine in conjunction with chemical therapy increases the ability of the vaccine to excite the cancer immune system.