Arimidex is a type of hormonal therapy used in the treatment of breast cancer in women who have had their menopause (change of life). Hormonal therapies interfere with the production or action of particular hormones in the body. Hormones are substances produced naturally in the body. They act as chemical messengers and help to control the activity of cells and organs.

There are several different types of hormonal therapy. Arimidex has been approved as a treatment for advanced breast cancer in postmenopausal women whose disease has progressed following therapy with tamoxifen.

Results from studies suggest that growth of some breast cancer tumors is stimulated by the female hormone estrogen. Arimidex, a nonsteroidal compound, is the first entry in a new class of third-generation selective oral aromatase inhibitors. Inhibition of aromatase reduces the production of estrogen. Thus, Arimidex reduces serum concentration of estrogen, an effect that has been shown to be of benefit in postmenopausal women with breast cancer.