Description

Approximately 70% of breast cancers express the oestrogen receptor (ER), and the majority of ER positive cancers respond to ER inhibition by tamoxifen. An alternative approach to tamoxifen in postmenopausal women is to induce oestrogen deprivation by inhibition of aromatase, which converts androgens to oestrogens. Third generation aromatase inhibitors (AIs) such as letrozole, anastrozole and exemestane reduce circulating oestrogen to undetectable levels and are active in postmenopausal women with ER positive tumours. In advanced breast cancer, trials have shown AIs to be more effective than progestins following tamoxifen failure, with improvements in response rates, time to progression and survival. In addition, recent studies have compared AIs with tamoxifen as first line endocrine therapy. These have shown improved time to progression for both anastrozole
1mg daily and letrozole 2.5mg daily when compared to tamoxifen. Ongoing studies will clarify the role of AIs in early breast cancer. Initial indications are that AIs are at least as effective as tamoxifen in the neoadjuvant (preoperative) setting. An AI should be considered standard treatment for postmenopausal women with ER positive metastatic breast cancer following tamoxifen failure, and aromatase inhibitors are replacing tamoxifen as the standard of care for first line endocrine therapy in this patient group.