Cancer vaccines are a promising way to outsmart cancer, especially when combined with other immune-stimulating drugs. Memorial Sloan Kettering doctors are working hard to make these and other immunotherapies more effective, for more people. Your immune system provides one of the best defenses against cancer. But sometimes it needs a little bit of help. That's because cancer cells are clever and find ways to evade attacks. Therapeutic cancer vaccines give your immune system a boost, helping it to find and fight cancer. These vaccines have two main ingredients: distinctive markers called antigens that distinguish cancer cells from normal cells and a chemical "red flag" called an adjuvant that alerts the immune system that cancer is present. When injected, this powerful combination jump-starts an immune response to the cancer. Immune cells can then find and destroy cancer cells in the body.