The goal of endocrine treatment is to block or interfere with the function of estrogen or progesterone. The major source of estrogen in premenopausal women is the ovaries. In premenopausal women with HR-positive advanced breast cancer, tamoxifen, ovarian function suppression or a combination of those have been used. Unfortunately, not all patients have a response to first-line endocrine therapy, and even patients who have a response will eventually become resistant. Patients experiencing disease progression with a first-line endocrine therapy may benefit from other endocrine agents, such as aromatase inhibitors (steroidal or nonsteroidal) and the estrogen receptor (ER) antagonist2-5. Aromatase inhibitors combined with luteinizing hormone-releasing hormone (LHRH) analogs or ovarian ablation are also a feasible treatment modality for premenopausal patients with HR-positive advanced breast cancer6.