Why do breast cancer patients need endocrine therapy? Known research tells us that the occurrence and development of breast cancer are closely related to estrogen, which opens the signaling pathway of tumor cells through binding with estrogen receptors, promoting the division and proliferation of tumor cells, and promoting the growth and development of tumors. The mechanism of endocrine therapy is clear: one is to reduce the production of estrogen, and the other is to prevent the already produced estrogen from working, thus reducing the recurrence of breast cancer. Endocrine therapy is an extremely important part of comprehensive breast cancer treatment. For premenopausal patients, estrogen is produced by the ovaries. The method to reduce estrogen production is to remove the ovaries, and the option is to remove the ovaries through laparoscopic surgery. Another method is to inhibit the function of the ovaries through drugs, the effect is equivalent to ovarian removal. Both methods have their advantages and disadvantages. Surgery is simple and effective, and the cost is low, but you will never get it back once it is removed. Choose drug inhibition, need long-term medication, 2-5 years, more trouble, high cost, but after stopping the drug will come back to menstruation, the impact on the quality of life is small. 2. For postmenopausal patients, estrogen is produced by the adrenal glands, which are then converted into estrogen through the action of aromatase. Therefore, the endocrine treatment method is to use aromatase inhibitors to inhibit the conversion of androgens, thus reducing the production of estrogen. There are three kinds of aromatase inhibitors we use, anastrozole (Reninde), letrozole (Flon, the domestic one is Fury) and exemestane (Anoxin), all of which have similar efficacy and toxic side effects. We know that the first step for estrogen to function is to bind to the estrogen receptor, and if the binding of the hormone to the receptor is blocked, estrogen cannot function. The most commonly used blocking agents are tamoxifen and toremifene (Cardinal), which have no significant differences in efficacy and toxic side effects. It has a slightly different mechanism of action from tamoxifen and toremifene. It can block the binding of estrogen and receptor while down-regulating the level of receptor, which has better efficacy than tamoxifen and toremifene, with the disadvantage that it is more expensive. Third, the new mechanism of action of drugs: 1, everolimus, mToR inhibitor, for patients with recurrent metastases, has better efficacy, domestic marketed. 2.PD0332991, CDK4/6 inhibitor, used for patients with advanced relapsed metastatic breast cancer, not yet available in China. IV. Progestins, megestrol acetate and medroxyprogesterone, are also an option for endocrine therapy. The main drugs that can be used before menopause are: tamoxifen, toremifene, goserelin, etc. The main drugs that can be used after menopause are aromatase inhibitors, fulvestrant, etc. Tamoxifen and Toremifene can also be used in the postmenopausal period. It is important to talk to the attending physician about which specific endocrine therapy drugs are needed for which patient. Most of the endocrine therapy needs to be carried out for 5 years, and some patients need 10 years of treatment period. Because endocrine therapy is extremely important in reducing recurrence and metastasis of breast cancer, it is important to adhere to treatment.