The development of endocrine therapy for breast cancer over one hundred years has resulted in a variety of endocrine therapy options: ovarian denervation, pharmacological denervation, triamcinolone, progesterone, aromatase inhibitors, fulvestrant, etc. Especially in recent years, with the successful development of third-generation aromatase inhibitors and the completion of several clinical studies of third-generation aromatase inhibitors with triamcinolone, third-generation aromatase inhibitors are increasingly becoming an important treatment option for hormone receptor-positive breast cancer patients. Adjuvant endocrine therapy for ER-positive early premenopausal breast cancer For patients with ER or PgR-positive breast cancer, adjuvant endocrine therapy is very important to reduce the risk of recurrence and prolong survival. Adjuvant endocrine therapy can reduce the risk of tumor recurrence by an average of 40%. Because of the significant efficacy and the majority of hormone receptor-positive patients, adjuvant endocrine therapy is presumed to reduce breast cancer mortality more than other treatments. In addition to preventing metastatic recurrence, adjuvant endocrine therapy also reduces the risk of ipsilateral or regional recurrence in the breast and reduces the risk of contralateral breast cancer. Based on these advantages, adjuvant endocrine therapy is recommended for all hormone receptor positive patients, regardless of tumor size and lymph node metastasis. Adjuvant endocrine therapy is effective only if ER or PgR is positive. If these receptors are not expressed, there is no clinical benefit from adjuvant endocrine therapy. This requires high-quality hormone receptor testing for all newly diagnosed breast cancers. Multiple prognostic factors have been found to be associated with the risk of recurrence in patients with ER-positive breast cancer. To date, however, no single factor other than hormone receptors has identified patients who would or would not benefit from adjuvant endocrine therapy. It is currently believed that ER-positive breast cancer has a different mechanism of recurrence than other breast cancers . Without endocrine therapy, there is a peak of recurrence at 2 to 5 years and then a stable and persistent risk of recurrence for at least 15 years. Adjuvant endocrine therapy can significantly reduce the early recurrence rate over 10 years. There is also a lag effect of endocrine therapy, such that after 5 years of endocrine therapy, the recurrence rate within 15 years can also be significantly reduced. Over time, secondary breast cancer and non-breast cancer deaths accounted for a significant proportion of adjuvant endocrine therapy adverse events. This suggests the need for long-term follow-up of patients receiving adjuvant endocrine therapy. Tamoxifen, an ER receptor modulator, has been shown in several prospective, randomized controlled trials to reduce breast cancer recurrence by approximately 40% and breast cancer mortality by approximately 20% over 5 years of endocrine therapy. Benefits of tamoxifen therapy can be obtained regardless of patient age and menstrual status. The ideal duration of tamoxifen therapy may be 5 years, and studies have shown no significant clinical benefit beyond 5 years of tamoxifen therapy. Side effects of tamoxifen include menopausal symptoms such as night sweats and irregular menstruation in premenstrual patients. Tamoxifen can mildly increase the incidence of uterine cancer and deep vein thrombosis, especially in postmenopausal patients. The quality of life of most patients using tamoxifen is not affected, and most patients can adhere to treatment. Adjuvant endocrine therapy for ER-positive early postmenopausal breast cancer Third-generation aromatase inhibitors (AIs) have ushered in a new era in the treatment of ER-positive early postmenopausal breast cancer. The mechanism of action of AIs is to prevent the conversion to estrogen by inhibiting aromatase, which reduces circulating estrogen by more than 90% from baseline levels. Because premenopausal women have residual ovarian function that upregulates ovarian aromatase expression in response to estrogen deprivation, AIs are a contraindication for premenopausal women. There have been several studies on the role of AIs in adjuvant endocrine therapy for early postmenopausal breast cancer. Since the standard of care in the past was 5 years of tamoxifen, most adjuvant trials have used AIs compared to 5 years of tamoxifen treatment. The comparison trials were divided into three categories: 1) initial treatment with AIs instead of tamoxifen; 2) sequential treatment: treatment with AIs after 2-3 years of tamoxifen; 3) extended treatment: continuation of AIs after completion of 5 years of tamoxifen treatment. These trials yielded important findings: first, sequential or prolonged treatment was associated with a reduced risk of breast cancer recurrence. The reduction in risk compared to tamoxifen alone was approximately 15% to 20%, and the absolute risk reduction was approximately 2% to 3% due to the better prognosis of early-stage breast cancer. The improved prognosis of breast cancer includes a reduced risk of distant metastatic recurrence, local recurrence and a reduction in contralateral breast cancer. Initial application of AIs therapy and sequential treatment with AIs had therapeutic benefit over initial application of tamoxifen therapy. Second, the BIG1-98 and TEAM trials did not find a difference between initial treatment with AIs and sequential treatment with AIs, and the ATAC trial did not find a difference between combined treatment with AIs and tamoxifen and treatment with tamoxifen alone. These findings recommend that AIs should be considered after a period of tamoxifen treatment, but the ideal timing of treatment change is unclear. The optimal duration of treatment with AIs is also unclear. The data show no difference in efficacy between 2.5 years and 5 years of treatment with AIs as initial therapy. Trials on the safety and efficacy of AIs beyond 5 years are ongoing. There are no trials comparing the difference in efficacy between one type of AI and another. Complications of AIs treatment: greater risk of accelerated osteoporosis and fractures after AIs treatment than in women taking tamoxifen; bisphosphonate treatment alleviates the reduction in bone salt density associated with AIs treatment; AIs treatment is associated with a unique arthralgia syndrome: manifested by muscle joint stiffness, pain; mild hypertension and hypercholesterolemia; possible long-term cardiac complications have not been elucidated. III. Neoadjuvant endocrine therapy for breast cancer The advent of systemic neoadjuvant therapy has turned surgically unresectable procedures into operable treatments, increasing breast conservation rates in patients with breast cancer that would otherwise require mastectomy. For premenopausal women, neoadjuvant chemotherapy is the current standard; however, for postmenopausal ER receptor-positive women, preoperative endocrine therapy with AI can improve breast conservation rates and reduce treatment-related toxicity. Specimens before and after neoadjuvant endocrine therapy facilitate the discovery of biomarkers and gene expression profiles that predict responsiveness to endocrine therapy and facilitate the evaluation of new drugs to improve the prognosis of ER-positive breast cancer. For ER-positive postmenopausal breast cancer with metastasis, locally advanced and early stage breast cancer, AIs therapy is superior to tamoxifen therapy. One of the first trials comparing AIs and tamoxifen in neoadjuvant therapy was the P024 trial, which used a randomized, double-blind, multicenter study of patients requiring breast-conserving therapy or inoperable patients treated with letrozole 2.5 mg/d or tamoxifen 20 mg/d for 4 months, with objective efficacy rates of 55% and 36%, respectively.The PROACT trial used anastrozole versus tamoxifen, with anastrozole No difference was found between anastrozole 1 mg/d or tamoxifen 20 mg/d for 3 months, with objective efficacy rates of 36% and 26%, respectively, after excluding chemotherapy patients (P=0.07). A meta-analysis of the P024, PROACT, IMPACT and exemestane trials found that the AIs were superior to tamoxifen in terms of objective clinical response rate, objective ultrasound response rate and breast conservation rate. the ACOSOGZ1031 trial directly compared the differences between the three AIs and the results have not been reported. Comparison of neoadjuvant chemotherapy and neoadjuvant endocrine therapy: The most effective treatment for ER-positive postmenopausal breast cancer is endocrine therapy. Genetic tagging of ER-positive postmenopausal breast cancer in multiple studies suggests the existence of a subgroup of patients with little benefit from chemotherapy, and these patients may have poor chemotherapy outcomes. However, it is noteworthy that neoadjuvant endocrine therapy alone has a low complete response rate (less than 5%), and neoadjuvant chemotherapy for ER-positive breast cancer also has a lower complete response rate than ER-negative breast cancer, with complete response rates of 3% and 17%, respectively, suggesting poorer efficacy of chemotherapy for ER-positive breast cancer. The only phase II study on neoadjuvant endocrine therapy and neoadjuvant chemotherapy using AIs (anastrozole and exemestane) versus adriamycin and paclitaxel chemotherapy for 12 weeks found no difference in overall objective response rate, complete response rate, mammography and ultrasonography response rate, and higher breast conservation rate in the endocrine therapy group. Endocrine therapy for advanced recurrent metastatic breast cancer The currently recommended endocrine therapeutic agents for the relief treatment of advanced breast cancer include: (1) estrogen receptor antagonists triamcinolone acetonide and toremifene. (2) Anastrozole and letrozole, non-steroidal aromatase inhibitors. (3) Non-steroidal aromatase inactivator exemestane. (4) Fulvestrant, an estrogen receptor modulator. (5) Progestins megestrol, methandrostenolone (6) Testosterone propionate, fluorometholone. The clinical benefit rates of first-line relief were 56-59% for anastrozole, 50% for letrozole, 67% for exemestane, and 38-55% for triamcinolone. Studies have shown that third-generation AIs are significantly better than triamcinolone in first-line rescue endocrine therapy, and there is still benefit from switching to another AIs after failure of one AIs. Overall, the later the drug is administered, the worse the efficacy, and it is appropriate to choose a drug with relatively high efficacy as early as possible. the FIRST trial showed that the TTP of fulvestrant compared to anastrozole in first-line treatment of advanced breast cancer was 23.4 months and 13.1 months, respectively, and fulvestrant was superior to anastrozole.