The occurrence and progression of breast cancer is related to the level of estrogen in the body and its metabolism. By changing estrogen levels or estrogen metabolic pathways, breast cancer can be effectively treated and recurrence can be prevented. As early as the late nineteenth century, bilateral oophorectomy was applied to treat advanced premenopausal breast cancer and was able to significantly prolong the survival of patients. In the 1970s, the introduction of triamcinolone acetonide became a new milestone in endocrine drug therapy for breast cancer, and several subsequent clinical studies established the status of triamcinolone acetonide as an endocrine therapy. The introduction of the third generation of aromatase inhibitors in the 1990s brought a new era of endocrine therapy for breast cancer, with many options for endocrine therapy and many questions for patients and physicians in the treatment process. Endocrine therapy plays a very important role in the post-operative adjuvant treatment of hormone-dependent recurrent metastatic breast cancer and early-stage breast cancer, and can even be used to prevent the occurrence of breast cancer in healthy women at high risk. Do I need endocrine therapy? Endocrine therapy can be considered as long as surgery or puncture pathology results show positive estrogen and progesterone receptors. Pre-operative neoadjuvant endocrine therapy can be another option for postmenopausal patients with positive hormone receptors, especially for those elderly patients who are not suitable for chemotherapy, and can be considered for surgical resection after shrinking the tumor through neoadjuvant endocrine therapy. Postoperative adjuvant is routinely treated with endocrine adjuvant therapy as long as estrogen and progesterone receptors are positive. Recurrent patients are mainly patients with slow progression or previous benefit from endocrine therapy, which have breast characteristics: 1. positive for hormone receptors (ER and/or PR); 2. long disease-free survival after surgery (time after surgery to first detection of recurrence); 3. only soft tissue and bone metastases, or asymptomatic visceral metastases such as non-diffuse lung metastases and liver metastases, with small tumor load and non-life-threatening Other visceral metastases that are not life-threatening; 4. Previous benefit from previous endocrine therapy. Endocrine therapy should be considered first as long as point 1 and any of points 2 to 4 are met. The choice of endocrine therapy still requires consultation with a physician, and endocrine therapy should not be self-administered or discontinued.