Aromatase inhibitors and breast cancer

These results indicate that first- and second-generation aromatase inhibitors may block peripheral aromatase by up to 90%, and markedly suppress circulating oestrogens (although levels may be detected in plasma even when high doses are given over a prolonged period). There is an extensive clinical experience in patients with breast cancer, particularly in postmenopausal women with advanced disease. Clinical benefits are similar to those of other endocrine therapies and are largely restricted to oestrogen receptor-positive tumours. Responses may be seen in patients relapsing on other endocrine therapies, and indeed previous endocrine-induced regression is predictive of sensitivity to aromatase inhibitors. Nevertheless, many of the early drugs lack specificity and potency. Tamoxifen, which produces fewer side-effects, has therefore been the preferred first-line hormone therapy for advanced or recurrent disease and in the adjuvant setting. The challenge has been to design new aromatase inhibitors with improved characteristics, and determine whether these translate into additional clinical benefits.