Endocrine therapy for breast cancer is a treatment to remove the effect of estrogen on the tumor by ovarian depot, competitive binding to estrogen receptors of cancer cells, and blocking the conversion of androgens to estrogen. Endocrine therapy for breast cancer can reduce the chance of tumor recurrence and metastasis. There may still be cancer cells remaining after surgery, so there is still a risk of recurrence and metastasis. Follow-up systemic treatment including endocrine therapy can prevent or delay the proliferation of these cancer cells and reduce the chance of tumor recurrence and metastasis. The advantages of endocrine therapy for breast cancer are as follows: the efficiency for patients with positive estrogen receptors and progesterone receptors can reach 60-80%. The toxic side effects of endocrine therapy drugs are less severe and less frequent, which is conducive to consolidation of treatment. Most of the endocrine therapies are administered orally and are suitable for long-term use, and the quality of life of patients during treatment is high. The common drugs used in endocrine therapy for breast cancer, such as tamoxifen, goserelin, treprostinil, leuprolide, anastrozole, letrozole and exemestane, are commonly used for this purpose in postmenopausal women as the ovaries stop secreting estrogen, and estrogen in the body comes from the conversion of androgens by the action of aromatase, so aromatase inhibitors are commonly used in postmenopausal patients. Duration of endocrine therapy for breast cancer, after surgery for early stage breast cancer patients, endocrine drug therapy can be started 3~4 weeks after finishing the last chemotherapy Currently, it is generally advocated to take 5 years.