The American Society of Clinical Oncology now says exemestane may benefit post-menopausal patients at increased risk of the disease.
The drug is not approved by the FDA for breast cancer prevention but a clinical trial shows it can reduce the risk by up to 70 percent compared with placebo.
The panel also strengthens the guidelines on tamoxifen and raloxifene use to decrease the development of breast cancer in at-risk women.
Details are in the Journal of Clinical Oncology.
