Safety of Elacestrant in ER+/HER2- and ESR1 Mutations MBC

Inclusion Criteria: * 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). Exclusion Criteria: * 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