A Study Comparing BL-B01D1 With Chemotherapy of Physician's Choice in Patients With Unresectable Locally Advanced, Recurrent, or Metastatic HR+HER2- Breast Cancer

Inclusion Criteria:

1. Voluntarily sign the informed consent and follow the requirements of the protocol;

2. No gender limit;

3. Age ≥18 years old;

4. expected survival time ≥3 months;

5. Patients with unresectable locally advanced, recurrent metastatic HR+HER2- breastcancer;

6. The subjects had received 1-2 lines of chemotherapy regimens in the unresectablelocally advanced recurrence or metastasis stage, and had been treated withendocrine, CDK4/6 inhibitors, and taxanes;

7. Documented radiographic disease progression;

8. Consent to provide archival tumor tissue samples or fresh tissue samples of primaryor metastatic lesions within 3 years;

9. Must have at least one measurable lesion according to RECIST v1.1 definition;

10. ECOG score 0 or 1;

11. Toxicity of previous antineoplastic therapy has returned to ≤ grade 1 defined byNCI-CTCAE v5.0;

12. No severe cardiac dysfunction, left ventricular ejection fraction ≥50%;

13. No blood transfusion, no use of cell growth factors and/or platelet raising drugswithin 14 days before screening, and the organ function level must meet therequirements;

14. Urine protein ≤2+ or < 1000mg/24h;

15. For premenopausal women with childbearing potential, a pregnancy test must beperformed within 7 days before the initiation of treatment, serum pregnancy must benegative, and it must be non-lactating; All enrolled patients (male or female) wereadvised to use adequate barrier contraception throughout the treatment cycle and for 6 months after the end of treatment.

Exclusion Criteria:

1. Prior receipt of an ADC drug with a topoisomerase I inhibitor as a toxin;

2. Prior receipt of an ADC or antibody drug targeting EGFR and/or HER3;

3. Chemotherapy, biological therapy, immunotherapy, etc., have been used within 4 weeksor 5 half-lives before the first dose, small molecule targeted therapy has been usedwithin 5 days, palliative radiotherapy, modern Chinese medicine preparationsapproved by NMPA for anti-tumor therapy, etc., have been used within 2 weeks;

4. anthracycline equivalent cumulative dose of adriamycin > 360 mg/m2;

5. History of severe cardiovascular or cerebrovascular disease;

6. Unstable deep vein thrombosis, arterial thrombosis, and pulmonary embolism requiringmedical intervention within 6 months before screening; Infusion-related thrombosiswas excluded;

7. QT prolongation, complete left bundle branch block, III degree atrioventricularblock, frequent and uncontrollable arrhythmia;

8. Other malignant tumors diagnosed within 3 years before the first dose;

9. Hypertension poorly controlled by two antihypertensive drugs; Patients with poorglycemic control;

10. A history of interstitial lung disease (ILD) requiring steroid therapy, current ILDor grade ≥2 radiation pneumonitis, or suspicion of such disease on imaging duringscreening;

11. Complicated pulmonary diseases leading to clinically severe respiratory functionimpairment;

12. Patients with active central nervous system metastases;

13. Patients with massive or symptomatic effusions or poorly controlled effusions;

14. Imaging examination showed that the tumor had invaded or wrapped around the largeblood vessels in the abdomen, chest, neck, and pharynx;

15. Severe infection within 4 weeks before randomization; Evidence of pulmonaryinfection or active pulmonary inflammation within 2 weeks before randomization;

16. Was receiving &gt before randomization; Long-term systemic corticosteroid therapywith 10mg/ day prednisone or equivalent anti-inflammatory active drugs or any formof immunosuppressive therapy;

17. Severe unhealed wound, ulcer, or fracture within 4 weeks before signing the informedconsent;

18. Subjects with clinically significant bleeding or obvious bleeding tendency within 4weeks before signing the informed consent;

19. Patients with inflammatory bowel disease, extensive bowel resection history, immuneenteritis history, intestinal obstruction or chronic diarrhea;

20. Have a history of allergy to recombinant humanized antibodies or to BL-B01D1 and anyexcipients; A history of autologous or allogeneic stem cell transplantation;

21. Human immunodeficiency virus antibody positive, active hepatitis B virus infectionor hepatitis C virus infection;

22. A history of severe neurological or psychiatric illness;

23. Received other unmarketed investigational drug or treatment within 4 weeks beforethe first dose; A live vaccine dose within 28 days before the planned dose or thefirst dose;

24. Any complications or other circumstances deemed by the investigator to precludeparticipation in the trial.