Anastrozole for Breast Cancer, commonly known by its brand name Arimidex, is a medication used primarily to treat breast cancer in women who have gone through menopause. It belongs to a class of drugs called aromatase inhibitors, which work by lowering the levels of estrogen in the body. Some breast cancers rely on estrogen to grow, so reducing its levels can help slow down or stop the growth of these cancers. Anastrozole blocks an enzyme called aromatase, which is responsible for producing estrogen in the ovaries and other tissues. By inhibiting this enzyme, anastrozole effectively reduces the amount of estrogen available, making it harder for estrogen-dependent tumors to thrive. This treatment is particularly effective for women with hormone receptor-positive (HR+) breast cancer, where the cancer cells have receptors that respond to estrogen. Anastrozole is typically prescribed for postmenopausal women with early-stage or advanced breast cancer that is HR+. It may also be used to lower the risk of developing breast cancer in women who are at high risk due to family history or genetic factors. The usual dosage is one milligram taken once daily, and treatment often lasts for about five years, although this can vary based on individual circumstances.