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.

A Multicenter, Open-label, Randomized Controlled Phase III Clinical Study Evaluating the Efficacy and Safety of HRS-8080 Combined With Dalpiciclib Versus Fulvestrant Combined With Dalpiciclib in Patients With Locally Advanced or Metastatic Breast Cancer Resistant to Adjuvant Endocrine Therapy.

The study is being conducted to evaluate the efficacy and safety of HRS-8080 combined with dalpiciclib versus fulvestrant combined with dalpiciclib in patients with locally advanced/metastatic breast cancer who had developed drug resistance to prior 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.