A new study has found that a drug currently used to prevent breast cancer can also prevent the disease from occurring. The drug, exemestane, is a type of compound known as an aromatase inhibitor. Aromatase inhibitors have been shown to prevent a recurrence of cancer after tumors have been surgically removed. Researchers have long suspected that aromatase inhibitors would also help prevent the initial occurrence of breast cancer, but this is the first big randomized study to actually show that. Two drugs, tamoxifen and raloxifene, are currently approved to prevent breast cancer, but they are rarely used because of their extreme side effects, which include uterine cancer. Exemestane does not have such side effects.