This study aims to evaluate the safety, tolerability, efficacy and pharmacokinetics of HRS-6208 in combination with HRS-8080 ± HRS-6209, or in combination with fulvestrant ± HRS-6209, or in combination with letrozole ± HRS-6209 in patients with advanced unresectable or metastatic breast cancer.

Inclusion Criteria:

1. Female, aged 18-75 (inclusive);
2. ECOG score 0-1;
3. Estimated survival time ≥ 12 weeks;
4. Possessing adequate bone marrow and organ function;
5. Participants of reproductive/childbearing potential must agree to take adequate and effective contraceptive measures from the time they sign the informed consent form, during the study treatment period, and up to 2 years after the last use of the trial medication;
6. Participants must provide informed consent for this study before the trial and voluntarily sign a written informed consent form.

Exclusion Criteria:

1. Within 5 years prior to the first dose of study medication, the occurrence of other malignancies, except for fully treated cervical carcinoma in situ, basal cell or squamous cell skin cancer, and post-radical surgery thyroid papillary carcinoma;
2. Active brain metastasis, carcinomatous meningitis, spinal cord compression, or history of primary central nervous system tumors;
3. Severe bone damage caused by tumor bone metastasis as determined by the investigator;
4. Adverse events caused by previous anti-tumor treatment have not been resolved;
5. Participants with one of multiple factors affecting oral medication;
6. History of severe cardiovascular and cerebrovascular diseases;
7. Presence of severe infections;
8. Significant clinically meaningful bleeding within 3 months prior to the first dose of study medication;
9. Active autoimmune diseases, history of immune deficiency, history of autoimmune diseases, or history of diseases or syndromes requiring systemic steroid hormone or immunosuppressive drug treatment, or acquired conditions (HIV infection), congenital immune deficiency diseases, or history of organ transplantation;
10. Active untreated hepatitis;
11. History of active tuberculosis infection within 1 year prior to enrollment, or history of active tuberculosis infection more than 1 year ago without standard treatment;
12. Washout period of prior drug or treatment did not meet protocol requirements before the first dose of study medication;
13. Prior use of prohibited drugs specified in the protocol;
14. Is pregnant or breastfeeding or planning to become pregnant within 2 years after the last dose of study medication;
15. History of clear neurological or psychiatric disorders, and participants with a history of psychiatric drug abuse or drug addiction;
16. Allergic reactions to any study drug or excipients;
17. Factors confirmed by the investigator as unsuitable for participation in this clinical study.