A cancer vaccine is a vaccine used to prevent or treat cancer. Preventive cancer vaccines, such as the HPV vaccine and the Hepatitis B vaccine, block infection of the causative agents, as do traditional vaccines such as polio vaccine. Therapeutic cancer vaccines, which are newer and chiefly experimental, coax a person's immune system into recognizing and destroying malignant cells without harming normal cells; they are being investigated for the treatment of breast, lung, colon, skin, kidney, prostate, and other cancers.