Exemestane is used to treat early breast cancer in women who have experienced menopause ('change of life'; end of monthly menstrual periods) and who have already been treated with a medication called tamoxifen (Nolvadex) for 2 to 3 years. This medication is also used to treat breast cancer in women whose breast cancer has worsened while they were taking tamoxifen. Exemestane is in a class of medications called aromatase inhibitors. It works by decreasing the amount of estrogen produced by the body. This can slow or stop the growth of some breast tumors that need estrogen to grow.