Hormone receptor-positive breast cancer accounts for about 70% of all breast cancers. Extended endocrine therapy with aromatase inhibitor is the current main treatment for hormone receptor-positive breast cancer. However, previous studies have shown a long-lasting risk of the recurrence of hormone receptor-positive breast cancer at early stage, and disease recurrence is considered inevitable only depending on a 5-year of adjuvant endocrine therapy. Therefore, extended endocrine therapy is considered as a possible measure to reduce the risk of recurrence. Numerous clinical studies have focused on extended endocrine therapy in patients with specific types of breast cancer. In 2017, the National Comprehensive Cancer Network (NCCN) updated the recommends for extended endocrine therapy with aromatase inhibitor, where postmenopausal early-stage breast cancer patients wo have high risk factors may be considered to be given an extended 5-year endocrine treatment with aromatase inhibitor after the initial 5-year treatment. In 2019, the Chinese Society of Clinical Oncology also suggested that postmenopausal hormone receptor-positive patients who have been well tolerated to the initial 5 years of adjuvant endocrine therapy can be given the extended endocrine therapy under some restrictions. However, extended endocrine therapy may also cause other risks in patients. Long-term tamoxifen treatment can significantly increase the incidence of adverse reactions such as endometrial cancer, thrombotic disease, and dyslipidemia, and long-term aromatase inhibitor treatment can also increase the incidence of osteoporosis, fractures, dyslipidemia, and hypertension. Although anti-cancer treatment can reduce cancer deaths, it may increase deaths due to cardiovascular diseases. An attempt has been proposed to find out an indicator that can effectively determine the necessity of extended endocrine therapy in such patients, not only improving the prognosis of breast cancer patients, but also reducing treatment-related side effects. The author's team recently discovered sj-subway, a possible factor with a long tubular structure in breast cancer lesions. The authors found that the higher expression of sj-subway indicates the worse patient's prognosis. So the positive expression of sj-subway may be a predictor of recurrence and metastasis in high-risk hormone receptor-positive patients. However, whether this predictor can be used clinically remains to be studied. This real-world study intends to analyze the difference in the clinical efficacy of extended endocrine therapy under different sj-subway expression in high-risk hormone receptor-positive breast cancer patients, and to explore whether sj-subway can screen out the patients who can benefit from extended endocrine therapy, thus providing a therapeutic help for hormone receptor-positive breast cancer patients.