Defining the role of aromatase inhibitors in the adjuvant endocrine treatment of early breast cancer

BACKGROUND: Over the past few years, data have been published concerning the relative efficacy and safety profiles of tamoxifen and the aromatase inhibitors (AIs) in the adjuvant therapy setting for women with early hormone receptor-positive breast cancer. Recently, debate has centred around trials which have studied primary tamoxifen and AI therapy, switching and sequencing strategies and extended adjuvant therapy. METHODS: Here, a group of 24 breast cancer experts review efficacy and safety data from the recent major trials investigating tamoxifen and the third-generation AIs in postmenopausal women, which have challenged the perception of tamoxifen as optimum adjuvant endocrine therapy. Data from the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial, Breast International Group (BIG) 1-98 study, National Cancer Institute of Canada MA 17 trial, Intergroup Exemestane Study (IES), Italian Tamoxifen Anastrozole (ITA) trial, Austrian Breast and Colorectal Cancer Study Group (ABCSG) Trial 8 and Arimidex-Nolvadex (ARNO) 95 are considered to provide a rational interpretation of the impact of these data on current practice, and to highlight areas where further investigation is needed. CONCLUSION: We can be confident that AIs represent superior adjuvant endocrine treatment to tamoxifen in postmenopausal women, either as initial therapy or as an alternative for women who have started adjuvant therapy with tamoxifen. However, there remain issues regarding the best way to use AIs, such as the optimal length of AI treatment and how a sequence of tamoxifen followed by an AI compares with AI monotherapy; these will require further data to resolve.