1\. must have a histologically or cytologically confirmed diagnosis of breast cancer with evidence of locally advanced disease unsuitable for excision or radical radiotherapy, or evidence of metastatic disease unsuitable for radical treatment.
2\. female ≥ 18 years of age
3\. female subjects must be postmenopausal (meeting any of the following criteria is sufficient) a) Has undergone oophorectomy. b) Age ≥ 60 years. c) 40 years old \< age ≤ 60 years old with 1 year of menopause. d) Age \<60 years and receiving ovarian suppression therapy.
4\. ER-positive and HER2-negative status and ESR1-mutation positive must be confirmed.
5\. must have progressed on at least one line of endocrine therapy prior to enrollment, including monotherapy or combination therapy.
6\. have normal organ function (as assessed by the investigator).
You may not be if
1\. women who are pregnant or breastfeeding
2\. known difficulties in tolerating oral medications, or conditions that interfere with the absorption of oral medications or allergies to medications and their excitements
3\. other conditions that make enrollment in the study unsuitable, at the discretion of the investigator
