In vitro
Anastrozole inhibits the enzyme aromatase, which is responsible for converting androgens to estrogens. Anastrozole binds reversibly to the aromatase enzyme through competitive inhibition. Elevated levels of estrogens may increase the severity of breast cancer, as sex hormones can cause hyperplasia and differentiation at estrogen receptor sites. Anastrozole is used to treat breast cancer after surgery and for metastases in post-menopausal women.