A Study to Evluate Efficacy and Safety of HRS-8080 Combined With Dalpiciclib in Patients With Advanced or Metastatic Breast Cancer Resistant to Adjuvant Endocrine Therapy.

Inclusion Criteria: 1. Women aged 18 - 75 years old; 2. Eastern Cooperative Oncology Group performance status (ECOG-PS) of 0 to 1; 3. Patients with histologically confirmed locally advanced or metastatic breast cancer; 4. Patients with prior adjuvant endocrine resistance following curative-intent surgery; 5. Menstrual status: postmenopausal, perimenopausal, or premenopausal; 6. Presence of evaluable lesions; 7. Organ function must meet required criteria. Exclusion Criteria: 1. Patients with rapidly progressing disease, as judged by the investigator to be unsuitable for endocrine therapy; 2. Patients who have previously received fulvestrant or other novel SERMs (excluding tamoxifen and toremifene); 3. Patients with uncontrolled brain metastases, carcinomatous meningitis, or spinal cord compression; 4. Patients with a history of clinically significant cardiovascular disease; 5. Participants who have not recovered from adverse effects caused by prior therapies; 6. Participants with a history of another malignancy within the past 5 years or currently having another malignancy; 7. Known hypersensitivity to HRS-8080, fulvestrant, dalpiciclib, or any of their components, etc.