Advances in adjuvant endocrine therapy for postmenopausal women

Hormone receptor-positive cancers are the most common tumor subtype among postmenopausal women with breast cancer. Despite substantial improvements in disease-free survival and overall survival with tamoxifen and chemotherapy, recurrences still occur, and may ultimately lead to death from breast cancer. Importantly, disease recurrence includes both early and late events, with over half of all recurrences detected more than 5 years from initial breast cancer diagnosis. In recent years, a number of large, randomized trials have evaluated the role of the aromatase inhibitors (AIs) in postmenopausal women with hormone receptor-positive breast cancer. These studies have tested one of three approaches: (1) an upfront AI, (2) a sequential approach after 2-3 years of tamoxifen, and (3) extended endocrine therapy beyond 5 years. Results of these studies have challenged the previous standard of a 5-year course of tamoxifen alone. While the AIs have become a standard component of treatment for most postmenopausal women, many questions remain as to how best tailor endocrine treatment to individual patients. In addition, despite the gains achieved with the AIs, many recurrences are not prevented, and novel strategies are urgently needed, particularly for those women at high risk of recurrence. In this article, we review the efficacy and toxicity data from the available trials of endocrine therapy in the postmenopausal setting. We outline controversies in choosing the optimal endocrine approach, and we discuss selected ongoing studies. Finally, we highlight future research directions, such as the need to understand host and tumor heterogeneity.