Exemestane is approved in order to treat postmenopausal women with advanced breast cancer or early-stage breast cancer that is ER+. The is used in those patients whose disease (cancer) has already been treated through tamoxifen. This agent is also being studied for treating the other types of cancer. Exemestane reduces the amount of estrogen formed by the body. This may block the growth of cancerous cells that require estrogen to grow. Exemestane specifically is a type of aromatase inhibitor.