Aromatase inhibitors as adjuvant therapy for postmenopausal patients with early stage breast cancer

Endocrine therapy of hormone receptor-positive breast tumors is widely used as palliative therapy for metastatic breast cancer and as adjuvant therapy for early stage breast cancer. Tamoxifen has been the definitive standard of hormonal therapies for the last 30 years because of its documented efficacy and reasonable safety profile. Based on encouraging results from trials utilizing the selective, third generation aromatase inhibitors (AIs) in metastatic breast cancer, a number of trials were designed to examine these agents as adjuvant therapies. Trials directly comparing AIs with tamoxifen have, to date, demonstrated superior disease-free-survival with AIs. Likewise, trials examining the use of AIs after tamoxifen have demonstrated better outcomes compared with tamoxifen alone. Additionally, letrozole has been demonstrated to result in superior disease-free-survival after 5 years of adjuvant tamoxifen, compared with no further therapy. In general, the AIs are tolerated at least as well as tamoxifen but decrease bone mineral density and increase osteoporosis due to their lack of estrogenic effects on bone. Based on the fact that AIs appear more effective at preventing contralateral breast cancers than tamoxifen, they are being examined as breast cancer preventives. Despite available data using the AIs as adjuvant therapies, many questions remain unanswered, and further trials will be needed to address these important issues.