Arimidex (chemical name: anastrozole) is a medication used to treat breast cancer in women after menopause. It is an aromatase inhibitor that works by reducing the amount of estrogen the body makes. Arimidex is approved for the initial treatment of postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer and for the treatment of postmenopausal women with advanced breast cancer that has progressed following treatment with tamoxifen. It is also approved for adjuvant treatment (treatment following surgery with or without radiation) of postmenopausal women with hormone receptor-positive early breast cancer. Patients with hormone receptor-negative disease and patients who did not previously respond to tamoxifen therapy rarely responded to Arimidex. Arimidex is taken orally, usually once a day, with or without food as directed by a doctor. It is important to talk to a doctor or health care professional before taking Arimidex, as only they can decide if it is right for a patient.