Breast cancer has become one of the major malignant tumors threatening women’s health. However, in stark contrast to the rising trend in the incidence of breast cancer, the mortality rate of breast cancer has begun to decline. More and more breast cancer patients are able to survive for a long time, not only thanks to the improvement in the rate of early diagnosis and early treatment of breast cancer, but also thanks to the clinical application of more and more therapeutic means. Today, we will talk about one of the very important systemic treatments – endocrine therapy. When talking about breast cancer treatment, it is impossible not to first briefly introduce the molecular pathologic typing that determines the direction of breast cancer treatment. According to molecular pathology, breast cancer can be categorized into four types (LuminalA, LuminalB, Her-2-positive and triple-negative). Among them, Luminal type patients are hormone receptor positive and suitable for endocrine therapy; Her-2 positive patients are suitable for anti-Her-2 targeted therapy; and chemotherapy is suitable for all types of breast cancer patients. As one of the three systemic treatments, endocrine therapy plays a pivotal role in the systemic treatment of hormone receptor positive breast cancer. 1.What is endocrine therapy Endocrine therapy is a treatment method to block tumor growth and reproduction by regulating the level of estrogen in the body or blocking the interaction with estrogen. Endocrine therapy has a history of more than 100 years since it was applied in clinic. At present, the endocrine therapy drugs commonly used in clinic mainly include: the first category is estrogen receptor antagonist, the representative drug is tamoxifen (triamcinolone acetonide), which can inhibit the action of normal estrogen in the body. The molecular structure of tamoxifen is similar to that of estrogen, and it can bind to the hormone receptors on the surface of breast cancer cells, thus preventing normal estrogen and progesterone from binding to the receptors in the body. The second type of drugs is aromatase inhibitors, representing drugs such as Flonase, Raninde, exemestane, etc. Aromatase is a kind of active enzyme necessary for the production of estrogen in women’s body, and inhibition of aromatase can effectively reduce the level of estrogen in the body, thus reducing its stimulating effect on cancer cells. The third category is luteinizing hormone-releasing hormone LH-RH analogs, represented by Norethindrone. Ovarian denervation is one of the main endocrine treatments for premenopausal breast cancer, especially the pharmacological ovarian denervation – luteinizing hormone-releasing hormone (LH-RH) analogues with good efficacy and restoration of ovarian function after stopping the drug, which has already replaced surgery and radiotherapy as one of the main therapeutic means of treating premenopausal breast cancer. About 70% of breast cancer patients are estrogen or progesterone receptor (HR)-positive, and endocrine therapy for these patients can be used throughout the clinical process of preoperative neoadjuvant therapy, postoperative adjuvant therapy, and rescue therapy after recurrence and metastasis. Compared with chemotherapy, endocrine therapy is characterized by mild adverse effects, relatively inexpensive, and easy to apply with the same certainty of efficacy. Therefore, the quality of life of patients receiving endocrine therapy is relatively high. The main purpose of preoperative neoadjuvant therapy is to rapidly reduce the stage, so that inoperable patients can become operable and patients who cannot keep their breasts can undergo breast-conserving surgery. Therefore, endocrine therapy, which is relatively mild in efficacy and slow in effect, is currently less clinically applied at this stage, and is partly used for inoperable patients with locally advanced breast cancer who are of advanced age or have severe underlying diseases and are not suitable for chemotherapy. The goal of operable breast cancer is cure. For hormone receptor-positive operable breast cancer patients, postoperative adjuvant endocrine therapy significantly reduces the recurrence rate, prolongs disease-free survival and overall survival, so its status is pivotal. Current guidelines generally recommend postoperative adjuvant endocrine therapy for 5-10 years, and even up to 15 years for patients at higher risk of recurrence. Longer medication duration means that patients have a way to prevent recurrence and a longer period of time without the possibility of recurrence. However, in clinical practice, many patients slacken off and relax their vigilance due to the long period of time, and discontinue the medication unreasonably due to a variety of reasons, resulting in recurrence and metastasis. Therefore, it is especially emphasized that in the process of long-term adjuvant endocrine therapy, any adverse reactions should be communicated with doctors in time, and should not stop medication without authorization, meanwhile, regular review is required to detect the signs of recurrence and metastasis in time. The earlier the recurrence and metastasis are detected, the lighter the tumor load will be, and the more favorable the treatment will be, so regular postoperative review is very important. The goal of metastatic breast cancer treatment is to prolong the survival time of patients while minimizing their pain and improving their quality of life. The advantages of endocrine therapy fit right into the treatment goal of advanced breast cancer. Therefore, endocrine therapy should be preferred for patients with advanced breast cancer who are hormone receptor-positive, have long disease-free intervals, slow tumor progression, and asymptomatic or mildly symptomatic visceral metastases. For any patient with hormone receptor-positive advanced breast cancer, the opportunity of endocrine therapy should be given when appropriate during the long course of treatment. The following case well illustrates the benefits of endocrine therapy: Yang, a 48-year-old female patient with hormone receptor-positive postoperative breast cancer with multiple bone metastases and lung metastases (small lesions and asymptomatic), was seen in March 2012, and was given first-line treatment with ovarian function inhibitor combined with anastrozole (endocrine therapy), and after the evaluation of the effectiveness of the treatment, the patient underwent a double oophorectomy in order to save money, and continued with the postoperative Anastrozole treatment, this one program for the patient nearly 4 years (45 months) of normal life after metastasis survival, which is difficult to do with chemotherapy. 3, endocrine therapy should attract the attention of breast doctors At present, there are still many doctors and patients who have limitations on the understanding of endocrine therapy, and they always think that chemotherapy is faster and better than endocrine therapy, and they give priority to chemotherapy for all patients, and even ignore the role of endocrine therapy during the whole treatment process of patients with metastatic breast cancer, which is very unfortunate. As a matter of fact, the efficacy of endocrine therapy in patients with hormone receptor positive endocrine therapy sensitivity is sometimes better than chemotherapy. This was the case in the following patient. A 65-year-old hormone receptor strong positive postoperative breast cancer patient Ms. Li, in December 2016, routine review found asymptomatic lung metastases, we recommended that the patient preferred endocrine therapy, but the patient refused, firmly requested chemotherapy, first-line 4 cycles of adequate chemotherapy, the efficacy of the evaluation of the stability of the lung lesions did not shrink instead of a slight increase in the lung lesions, and the patient self-conscious of the adverse effects can not continue to tolerate. She agreed to take oral letrozole as per our suggestion for the second line application of endocrine therapy, and the lung lesions disappeared after 3 months, and she has been taking the drug continuously for nearly 20 months now, and the old lady is very happy. Under the premise of good efficacy, normal life is not affected, and the cost of treatment is low, no other treatment has such advantages as endocrine therapy. Therefore, for patients with hormone receptor-positive metastatic breast cancer, endocrine therapy is as important as chemotherapy. Applying different treatments appropriately is like walking on two legs, which will make the patient walk longer and farther.