Sequencing of Endocrine Therapies in Breast Cancer – Integration of Recent Data

Abstract

A wide range of endocrine therapies has demonstrated activity in the treatment of hormone receptor-positive metastatic breast cancer and sequential tumor responses to sequential hormonal therapies are common. However, the optimal sequence of the hormonal therapies has not yet been determined. The selection of endocrine therapies in women with hormone receptor-positive breast cancer is strongly influenced by the menopausal status of the patient. For premenopausal women, tamoxifen alone or combined with ovarian suppression using a luteinizing hormone-releasing hormone (LHRH) agonist – such as goserelin or leuprolide – is an appropriate first-line hormonal therapy. Ovarian ablation or megestrol acetate is an appropriate second-line hormonal therapy for premenopausal women treated with tamoxifen as first-line therapy, or ovarian ablation plus an aromatase inhibitor (AI) or megestrol acetate for women treated with first-line tamoxifen plus an LHRH agonist. For postmenopausal women, the non-steroidal AIs anastrozole and letrozole now represent the preferred first-line hormonal treatment for metastatic breast cancer, based upon both efficacy and toxicity considerations. For second-line therapy in postmenopausal women, a number of options now exist, including tamoxifen, the steroidal AI exemestane, and the new agent fulvestrant. Fulvestrant, a novel estrogen receptor (ER) antagonist that downregulates the ER and has no known agonist effects, has been demonstrated to be at least as effective as anastrozole in postmenopausal women whose tumors progress on tamoxifen. The establishment of the optimal sequence of the endocrine therapies should offer significant benefits to women with hormone-sensitive metastatic breast cancer.