A review of the treatment of endocrine responsive metastatic breast cancer in postmenopausal women

Endocrine therapy is the corner stone treatment for postmenopausal women with hormone receptor-positive metastatic breast cancer (MBC). Besides tamoxifen and many older agents, recently developed endocrine agents for the treatment of MBC include the third generation aromatase inhibitors (AI) - anastrozole, exemestane, letrozole - and the pure oestrogen receptor antagonist fulvestrant. As treatment of breast cancer evolves, both tamoxifen and the AIs are being increasingly used in the adjuvant setting. As such, a significant proportion of patients with hormone receptor-positive MBC will have previously received tamoxifen, an AI or both, as adjuvant treatment. This has changed the metastatic landscape and has an impact on treatment choices for patients with hormone receptor-positive MBC. In this review, we evaluate the available evidence supporting the use of endocrine therapy for the treatment of hormone receptor-positive MBC. Additionally, we consider the effect of prior adjuvant therapy on treatment choice in the metastatic setting and the optimal treatment sequence. Finally, we discuss endocrine-responsive HER2 positive tumours and the ongoing research initiatives which aim to improve outcomes for patients with MBC.