Switching from tamoxifen to aromatase inhibitors for adjuvant endocrine therapy in postmenopausal patients with early breast cancer.

The third-generation aromatase inhibitors (AIs), including anastrozole, exemestane and letrozole, have demonstrated improved efficacy versus tamoxifen for the adjuvant endocrine treatment of postmenopausal patients with hormone receptor-positive breast cancer. AIs can be used in several adjuvant endocrine settings: as upfront therapy, switch to an AI after 2-3years of tamoxifen or extended therapy following 5years of tamoxifen. In the switch setting, two different types of study designs have been utilized. One is a late randomization design which randomizes patients who are disease-free after 2-3years of tamoxifen to receive an AI versus continuation of tamoxifen. In contrast, an early randomization design randomizes all patients immediately after primary treatment and prior to starting tamoxifen. Efficacy benefits with AIs have been shown in several trials evaluating the late randomization strategy, including the Intergroup Exemestane Study, the Italian Tamoxifen Anastrozole trial and the Anastrozole-Nolvadex 95 trial. Similarly, early randomization studies, including the Austrian Breast and Colorectal Cancer Study Group-8 and the Breast International Group (BIG) 1-98 trial, have demonstrated the effectiveness of receiving an AI after tamoxifen. Two trials are assessing an early switch strategy versus upfront AI therapy: the BIG 1-98 trial and the ongoing Tamoxifen Exemestane Adjuvant Multicentre trial are assessing switching from tamoxifen to an AI after 2-3years versus upfront AI therapy. This paper reviews studies that have investigated a switch strategy with AIs and considers the implications of these data on treatment choice for postmenopausal patients with hormone receptor-positive breast cancer.