Anastrozole (CAS 120511-73-1) is a synthetic non-steroidal aromatase inhibitor with molecular formula C₁₇H₁₉N₅ and molecular weight 293.37 g/mol. It is primarily used in the treatment of hormone receptor-positive breast cancer in postmenopausal women. It works by inhibiting the aromatase enzyme, which reduces the production of estrogen in the body, thereby depriving estrogen-dependent breast cancer cells of the hormone necessary for growth. By lowering estrogen levels, it helps slow or stop the progression of cancer. It is often prescribed as an adjuvant therapy following surgery or other primary treatments, such as chemotherapy, to reduce the risk of cancer recurrence. Additionally, it is used to treat advanced breast cancer that has metastasized to other parts of the body. Anastrozole may also be utilized in off-label scenarios, such as managing gynecomastia in men or as part of fertility treatments to control estrogen levels. In laboratory and pharmaceutical research, high-purity Anastrozole (≥99%) serves as a reference standard. Its effectiveness and tolerability make it a key component in hormonal therapy for breast cancer management.