An experimental breast cancer vaccine, developed by Dr. Leisha Emens at the Johns Hopkins Kimmel Cancer Center, is currently being tested in clinical trials. It acts by activating the immune system and lead immune cells, typically unable to detect cancer, to attack the cancer cells in the breast and throughout the body. Early vaccine studies, including a modest, but real improvement in survival time, show promising results, according to John Hopkins Medicine. A vaccine is not on the market, yet, but there are several things you can do to lower your risk of breast cancer.