Letrozole is a new generation of aromatase inhibitor, which is a synthetic benzyl triazole derivative. By inhibiting aromatase, letrozole reduces estrogen levels, thereby eliminating the Chemicalbook stimulating effect of estrogen on tumor growth. Studies in vivo and in vitro have shown that letrozole effectively inhibits the conversion of androgens to estrogen, which in postmenopausal women is mainly derived from the aromatization of peripheral tissues of androgen precursors.