Which medications in the drug class Aromatase Inhibitors are used in the treatment of Breast Cancer?

Updated: Dec 27, 2019
  • Author: Pavani Chalasani, MD, MPH; Chief Editor: John V Kiluk, MD, FACS  more...
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Answer

Aromatase Inhibitors

Aromatase inhibitors play a role in adjuvant therapy in breast cancer. These agents work by inhibiting aromatase, the enzyme responsible for converting other steroid hormones into estrogen. All 3 selective aromatase inhibitors (anastrozole, letrozole, and exemestane) have similar antitumor efficacy and similar toxicity profiles.

Anastrozole (Arimidex)

Anastrozole significantly lowers serum estradiol concentrations by inhibiting the conversion of adrenally generated androstenedione to estrone. It is used as first-line treatment of breast cancer in postmenopausal women with hormone receptor–positive or hormone receptor–unknown locally advanced or metastatic disease. It is also used to treat advanced breast cancer in postmenopausal women with disease progression after tamoxifen therapy.

Letrozole (Femara)

Letrozole is a nonsteroidal competitive inhibitor of the aromatase enzyme system. It inhibits the conversion of androgens to estrogens. Letrozole is indicated for adjuvant treatment of postmenopausal women with hormone receptor–positive early breast cancer. It is also used for first-line treatment of postmenopausal women with hormone receptor–positive or hormone receptor–unknown locally advanced or metastatic breast cancer.

Letrozole is also indicated for treatment of advanced breast cancer in postmenopausal women with disease progression after antiestrogen therapy and for extended adjuvant treatment of early breast cancer in postmenopausal women who have received 5 years of adjuvant tamoxifen therapy. [146]

Exemestane (Aromasin)

Exemestane elicits irreversible steroidal aromatase inactivation by acting as a false substrate for the aromatase enzyme. It binds irreversibly to the aromatase enzyme active site, causing inactivation (ie, suicide inhibition). It significantly lowers circulating estrogen concentrations in postmenopausal women.

Exemestane differs from tamoxifen in that it inhibits estrogen production, whereas tamoxifen inhibits estrogen at the receptor site. It may be superior to tamoxifen for breast cancer chemoprevention, with a better safety profile. However, exemestane is not yet indicated for this application by the American Society of Clinical Oncology (ASCO). It is indicated for advanced breast cancer in postmenopausal women whose disease has progressed after tamoxifen therapy. Off-label use of exemestane is suggested as an alternative to tamoxifen or raloxifene in the 2013 ASCO guidelines to reduce the risk of ER-positive breast cancer in high-risk postmenopausal women. [135]


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