Fulvestrant is a new competitive, “pure” estrogen receptor antagonist with the following characteristics: 1. After binding, it can block ER signaling pathway, rapidly downregulate and degrade tumor ER, and also significantly downregulate the expression level of PR (progesterone receptor); 2. The downregulation of ER in tumors is dose-dependent; 3. In vitro and in vitro studies have confirmed that it is still effective in TAM-resistant tumors; 4. Early clinical studies have shown that for postmenopausal Early clinical studies have shown that for late postmenopausal breast cancer, tolerability is similar to TAM, with differences in adverse effects, with fulvestrant not causing endometrial proliferation (no estrogen-like effects) and a low incidence of hot flashes (no entry into the central nervous system). In two randomized controlled phase III clinical studies, 0020 (North America, double-blind) and 0021 (Europe, open), the efficacy of fulvestrant (250 mg once monthly) was demonstrated to be similar to that of anastrozole (1 mg daily) in postmenopausal hormone receptor-positive metastatic breast cancer patients who had received prior adjuvant anti-estrogen or progestin therapy or had failed first-line endocrine therapy after metastasis. The overall incidence of adverse events was similar and the most common adverse reactions included injection site reactions (5-13%), followed by malaise, elevated liver enzymes (ALT, AST, ALP), nausea, headache, and also hot flashes, vomiting, diarrhea, anorexia, rash, urinary tract infections, joint disorders, thrombotic events/ischemic cardiovascular disorders, and allergic reactions. Most of the adverse events were mild and transient, with a significantly lower incidence of joint disease in the fluvastatin group than in the anastrozole group (p=0.0234). Based on these studies, fulvestrant (250 mg) was launched in the United States in 2002 and in Europe in 2004, and a similar double-blind randomized controlled clinical study (D6997L00004) was completed in China in 2010, with a TTP (time to disease progression) of 110 days, ORR (overall effectiveness rate) of 10% (8/121), and CBR (clinical benefit rate) of 36% in the fulvestrant group. The CBR (clinical benefit rate) was 36%, which was not statistically different from that of the anastrozole group. Accordingly, in March 2011, fulvestrant (250 mg) was approved by SFDA for marketing in China. The current indication in China is locally advanced or metastatic estrogen receptor-positive breast cancer that has recurred after or during adjuvant anti-estrogen therapy, or has progressed during anti-estrogen therapy. Preclinical and phase I and II clinical studies have found a dose-dependent efficacy of fulvestrant, with 500 mg suppressing ER, PR and Ki-67 levels more significantly than 250 mg. Studies comparing three dosing regimens of flovisetron 250mg/month (approved dose AD); loading dose (LD) 500mg day 0, 250mg day 14,28, followed by 250mg/month; and high dose (HD) 500mg day 0, 500mg day 14 followed by 500mg/month, showed that LD and HD reached steady state concentrations faster than AD. . In the phase III CONFIRM study, fulvestrant 500 mg significantly and clinically meaningfully prolonged PFS (progression-free survival) compared to fulvestrant 250 mg in postmenopausal hormone receptor-positive breast cancer patients who had failed prior endocrine therapy (median PFS: 6.5 months vs. 5.5 months; HR=0.80; 95% CI 0.68,0.94; p= 0.006), without any increase in adverse events or new safety events due to dose increases. Fulvestrant 500 mg has been approved in the United States, the European Union, and Japan since September 2010. Combined with the experience of current clinical trials and the pharmacokinetic characteristics of fulvestrant, monthly follow-up visits are now mostly conducted during the first 3 months of dosing to observe the general status of patients, monitor adverse reactions, and relevant tumor markers, and evaluate the efficacy every 3 months. In addition to the 0020/0021 study, several clinical studies have confirmed the role of fulvestrant in first-, second-, and multiline endocrine therapy for postmenopausal (including artificial menopause) hormone receptor-positive recurrent metastatic breast cancer. 2010 SABCS (San Antonio Breast Cancer Conference) reported that the FIRST study showed that fulvestrant (HD) significantly prolonged PFS compared to anastrozole in advanced first-line treatment. The EFECT study showed that fulvestrant (LD) was as effective as exemestane and well-tolerated in patients who failed NSAIDs. Vergote et al. reported that fulvestrant progression followed by other endocrine therapies, including AIs, still resulted in clinical benefit in some patients, thereby delaying the start of chemotherapy. A phase III randomized clinical study of fulvestrant in combination with anastrozole versus anastrozole alone in first-line treatment of postmenopausal recurrent metastatic breast cancer (SWOG S0226) was reported at the San Antonio Breast Cancer Conference in December 2011. Based on prior studies that fulvestrant is more active at low estrogen levels and that the combination of the two agents can downregulate a range of resistance proteins, the study was proposed to see if the combination of the two agents has a synergistic effect and can be crossed over to the combination arm after treatment failure in the anastrozole monotherapy arm. In this study, adverse effects were mostly tolerable, with an incidence of grade 3 or higher adverse effects of 14.5% and 12.7% , and no statistical difference between the two groups, but there were three treatment-related deaths in the combination group (two for pulmonary embolism and one for ischemic encephalopathy). The efficacy results showed a median PFS of 15 and 13.5 months for the fulvestrant (500 mg day 0, 250 mg day 14,28, and subsequent 250 mg/month) combined with anastrozole 1 mg treatment group and the monotherapy group, respectively (p=0.0145; HR=0.81, 95% CI 0.68-0.96), and further subgroup analysis showed an improvement in PFS in OS (overall survival) was also significantly superior in the combination treatment group, (47.7 months versus 41.3 months, p= 0.049;), and again, subgroup analysis showed that improvement in OS was significant in patients previously untreated with TAM, but not in patients treated with TAM-treated patients showed no significant difference. This study suggests that fulvestrant in combination with anastrozole prolongs PFS and OS, and therefore the combination is expected to become a new standard of care for first-line endocrine therapy in hormone receptor-positive advanced breast cancer. Fulvestrant offers a new drug option for endocrine therapy in advanced postmenopausal breast cancer patients that is safe and well tolerated, extending the time to benefit from endocrine therapy and delaying the start of treatment with cytotoxic drugs. Further clinical studies are needed to explore and observe the optimal regimen, efficacy and safety of fulvestrant in all stages of endocrine therapy for hormone receptor-positive breast cancer, and in particular to collect data on Chinese patients.