Beatson’s historic observations on the regression of breast cancer following oophorectomy over 100 years ago provided the first insight into the estrogen-dependent nature of breast cancer1). Endocrine therapy has become the treatment of choice for many patients with metastatic breast cancer. Selective targeting of the estrogen receptor pathway provides a more favorable benefit to toxicity ratio compared with systemic chemotherapy. Improvements in survival from first relapse with metastatic breast cancer have occurred over the last decades due to the development of newer more effective endocrine therapy and chemotherapy2, 3). The evolution of adjuvant endocrine therapy for breast cancer also continues to improve the outcome of patients with early stage breast cancer.