Letrozole.

IMPORTANCE OF THE FIELD: Aromatase is an enzyme which converts adrenal androgens to estrogens in postmenopausal women. Given the importance of estrogens in breast cancer growth, aromatase inhibitors are used to treat breast cancer in different settings. This review focuses on letrozole, a third generation aromatase inhibitor, encompassing pharmacodynamic and pharmacokinetic aspects as well as its clinical efficacy and safety. AREAS COVERED IN THIS REVIEW: A literature search and review of the studies published on letrozole were carried out using the MEDLINE database up to November 2009. WHAT THE READER WILL GAIN: The paper provides the reader with information about pharmacodynamic and pharmacokinetic aspects of letrozole, its preclinical and clinical efficacy and its safety. TAKE HOME MESSAGE: Letrozole is a well-tolerated and effective drug in metastatic breast cancer in postmenopausal women. Two clinical trials conducted in early breast cancer have confirmed its role in the adjuvant setting in postmenopausal women. More recently, data have confirmed its efficacy as neoadjuvant treatment in breast cancer. Future developments include the combination of letrozole with new biologic agents and tailoring of treatment with gene expression profiling studies.