Endocrine therapy has a firm role in adjuvant treatment of women with hormone receptor–positive invasive breast cancer. Until recently, tamoxifen was the most commonly used adjuvant endocrine therapy in premenopausal and postmenopausal women. Several randomized clinical trials have studied the third-generation selective aromatase inhibitors (AIs) (anastrozole, letrozole, and exemestane) as adjuvant endocrine therapy in postmenopausal women. These studies compared therapy with an AI alone versus tamoxifen alone; 2 to 3 years of tamoxifen followed by switching to an AI versus continuation of tamoxifen; or extended therapy with an AI after approximately 5 years of tamoxifen therapy. No statistically significant differences in overall survival were observed. A single trial using extended treatment with an adjuvant AI suggests a small, statistically significant survival advantage in women with axillary lymph node–positive disease while showing no statistically significant decrease in survival with the use of an AI. The toxicities of the AIs are generally acceptable, with fewer endometrial cancers, gynecologic complaints, and thromboembolic events, but more bone fractures and arthralgias compared with tamoxifen alone. Three widely disseminated treatment guidelines, the National Comprehensive Cancer Network Breast Cancer Clinical Practice Guidelines in Oncology, the American Society of Clinical Oncology Technology Assessment on the Use of Aromatase Inhibitors, and the St Gallen International Expert Consensus on the Primary Therapy of Early Breast Cancer, now incorporate AIs in the adjuvant therapy of postmenopausal women with estrogen receptor–positive breast cancer.
Robert W. Carlson, Clifford A. Hudis, and Kathy I. Pritchard
Jennifer A. Ligibel and Eric P. Winer
Adjuvant hormonal therapy has been shown to decrease the risk of breast cancer recurrence and overall mortality in patients with hormone receptor-positive breast cancer. Tamoxifen has been used in this setting for many years, both in premenopausal and postmenopausal patients. Tamoxifen is not devoid of toxicity, and attempts have been made to develop newer hormonal agents with better efficacy and less toxicity. The aromatase inhibitors have shown equivalent or superior efficacy to tamoxifen in the treatment of metastatic breast cancer, and efforts are underway to determine the role of these agents in early breast cancer. The ATAC trial recently showed that use of the third-generation aromatase inhibitor anastrozole in the adjuvant setting led to a modest improvement in relapse-free survival as compared with tamoxifen. Patients treated with anastrozole were also less likely to develop uterine cancer or experience a thromboembolic event. However, patients treated with anastrozole were more likely than those treated with tamoxifen to suffer a fracture or other musculosketal problem. An ASCO technology assessment panel reviewed the relevant data and issued a consensus statement regarding the use of aromatase inhibitors in the adjuvant setting. In general, the panel favored the continued use of tamoxifen as adjuvant hormonal therapy for most postmenopausal women. Within the next few years, further data from the ATAC trial and from other trials of aromatase inhibitors in the adjuvant setting should be available to guide treatment recommendations for this patient population.