<p>Anastrazole exerts its anti-estrogenic effects via selective and competitive inhibition of the aromatase enzyme found predominantly in the adrenal glands, liver, and fatty tissues. Many breast cancers are hormone receptor-positive, meaning their growth is stimulated and/or maintained by the presence of hormones such as estrogen or progesterone. In postmenopausal women, estrogen is primarily derived from the conversion of adrenally-produced androgens into estrogens by the aromatase enzyme- by competitively inhibiting the biosynthesis of estrogen at these enzymes, anastrozole effectively suppresses circulating estrogen levels and, subsequently, the growth of hormone receptor-positive tumours.</p>