Anastrozole (Arimidex) in clinical practice versus the old 'gold standard', tamoxifen

Abstract

For the past 25 years, the estrogen antagonist tamoxifen has been considered the 'gold standard' for the treatment of breast cancer, despite certain tolerability issues and the risk of developing resistance. The aromatase inhibitors work by blocking the conversion of androgens to estrogen and were developed for use in patients where ovarian function had ceased (naturally, surgically or pharmacologically). Anastrozole, a third-generation nonsteroidal aromatase inhibitor that is a highly potent and selective inhibitor of the aromatase enzyme, has been shown to be superior to the gold standard tamoxifen for the first-line treatment of postmenopausal women with advanced breast cancer. As second-line therapy, anastrozole has shown superior survival compared with megestrol acetate and is also efficacious as neoadjuvant treatment in postmenopausal women and in combination with goserelin for the treatment of premenopausal women with advanced breast cancer. More recently, the results of the ATAC (anastrozole, tamoxifen, alone or in combination) trial, a large study in 9366 patients, demonstrated that anastrozole was significantly superior to tamoxifen for the treatment of postmenopausal women with early breast cancer, with regards to disease-free survival (p = 0.013) and incidence of contralateral breast cancer (p = 0.007). In addition, anastrozole was shown to be significantly better tolerated than tamoxifen with respect to endometrial cancer (p = 0.02), vaginal bleeding/discharge (p < 0.0001 for both), ischaemic cerebrovascular events (p = 0.0006), thromboembolic events (p = 0.0006) and hot flushes (p < 0.0001), while tamoxifen was associated with significantly less musculoskeletal disorders and fractures than anastrozole (p < 0.0001 for both). This review focuses on both the clinical pharmacology and the clinical data of anastrozole with emphasis on its future applications.