Study of ADCs Combined With Adebrelimab in HER2-negative Advanced Breast Cancer

Inclusion Criteria: 1. 18 years to 75 years old (including boundary values); 2. ECOG PS Score: 0\~1; 3. Histologically or cytologically confirmed HER2-negative advanced breast cancer; 4. Disease progression after prior ≥1 line of systemic therapy; if HR-positive, prior CDK4/6 inhibitor is necessary; 5. Based on RECIST v1.1, at least one measurable lesion; 6. Brain metastasis with no clinical symptoms, or treated, stable brain metastases are eligible; 7. Patients must have a life expectancy ≥ 6 months; 8. Adequate organ function and marrow function (no corrective treatment within 14 days before first dose); 9. Women of childbearing potential should have a negative urine or serum pregnancy, and must promise to use an adequate method of contraception starting with the first dose of study therapy through 6 months after the last dose of study therapy or be celibate; Men who are not surgically sterile (including those sterilized by methods other than bilateral orchiectomy \[e.g., vasectomy\]) and who intend to have sexual intercourse with female partners of childbearing potential must use a contraceptive method from enrollment, throughout the study, and for 6 months after the end of the study to prevent partner pregnancy; 10. Available blood samples for ctDNA detection in the exploratory study; 11. Willing and able to provide written informed consent and comply with the requirements and restrictions in the protocol. Exclusion Criteria: 1. Has known active brain metastasis which needs local therapy immediately; 2. Prior use of ADCs with the same target as study drugs; 3. Existence of third space fluid that is not well controlled by effective methods, e.g. drainage; 4. Has received antitumor surgery, radiotherapy, chemotherapy, targeted therapy or immunological therapy within 4 weeks before first dose of study therapy; has received antitumor endocrine therapy within one week before first dose of study therapy; 5. Use of other antitumor systemic treatment during the study; 6. Has active autoimmune disease or a history of autoimmune disease; 7. Known history of immunodeficiency, including HIV-positive, other acquired or innate immunodeficient disease, or known history of organ transplantation; 8. Has active hepatitis B (HBsAg-positive and HBV DNA≥500 IU/mL), hepatitis C (positive for HCV antibody and HCV RNA above ULN) and hepatic cirrhosis; 9. Has an active infection requiring antibiotics, antiviral or antifungal treatment, or pyrexia \>38.5℃ of unknown origin during the screening period before first dose of study therapy (patients with pyrexia due to cancer could be enrolled determined by investigator); 10. Receiving immunosuppressive medication, or systemic corticosteroid therapy for the purpose of immunosuppression (prednisone at \>10mg/d or equivalent dose of other corticosteroids), and continuous use within 2 weeks before the first dose of study therapy; 11. Other malignancy within prior 5 years unless curatively treated with no evidence of disease for at least recent 3 years, except: curatively treated in situ cancer of the cervix, skin basal cell carcinoma or skin squamous cell carcinoma; 12. Hypersensitivity to study therapy or any of its excipients; 13. Has known clinically significant lung disease, including but not limited to: interstitial lung disease, pneumonitis, pulmonary fibrosis; 14. Known history of uncontrolled cardiovascular clinical symptom or disease that is not well controlled; 15. Has received a live vaccine within 4 weeks before first dose of study therapy, or potential to receive a live vaccine during the trial treatment; 16. Women with a positive serum or urine pregnancy test or who are breastfeeding; patients of childbearing potential who are unwilling or not available to use an effective method of contraception; 17. Other conditions that might influence the study and analysis of results in the opinion of the investigator.