Optimal adjuvant hormonal therapy in postmenopausal women with hormone-receptor-positive early breast cancer: have we answered the question?

Adjuvant endocrine therapy is the most important systemic treatment for postmenopausal women with hormone-receptor-positive early breast cancer following surgery. Most trials have shown that the third-generation aromatase inhibitors, anastrozole, letrozole (LET), and exemestane, significantly prolong disease-free survival compared with tamoxifen. However, an overall survival benefit with aromatase inhibitors was observed in only three trials to date, in retrospective analyses from selected groups of patients: sequential analysis in the Austrian Breast & Colorectal Study Group 8, switch analysis in the Intergroup Exemestane Study, and analysis of initial letrozole in Breast International Group 1–98 study. Although the priming effect observed in preclinical models and breast cancer patients provides a rationale for sequencing adjuvant endocrine treatment with tamoxifen and aromatase inhibitors, the optimal strategy for adjuvant endocrine treatment has yet to be determined. This review discusses aromatase inhibitor monotherapy, sequential adjuvant treatment with tamoxifen followed by an aromatase inhibitor, and sequential adjuvant treatment with an aromatase inhibitor followed by tamoxifen. Available data in support of and against each strategy is evaluated. The safety profiles of tamoxifen and aromatase inhibitors is also examined.