A Study Comparing BL-M07D1 With T-DM1 in Patients With Unresectable Locally Advanced or Metastatic HER2-positive 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 and ≤75 years old at the time of signing the informed consent; 4. expected survival time ≥3 months; 5. Patients with histologically or cytologically confirmed, unresectable, locally advanced or metastatic HER2-positive breast cancer; 6. Provide the latest tumor tissues to the central laboratory for HER2 and HR detection; 7. Must have at least one measurable target lesion that meets the RECIST v1.1 definition; 8. ECOG 0 or 1; 9. Toxicity of previous antineoplastic therapy has returned to ≤ grade 1 defined by NCI-CTCAE v5.0; 10. No severe cardiac dysfunction, left ventricular ejection fraction ≥50%; 11. Blood transfusion is not allowed within 14 days before the first use of the study drug, and no cell growth factor is allowed; 12. Coagulation function: international normalized ratio (INR) ≤1.5 and activated partial thromboplastin time (APTT)≤1.5×ULN; 13. Urine protein ≤2+ or \< 1000mg/24h; 14. For premenopausal women with childbearing potential, a pregnancy test must be performed within 7 days before the initiation of treatment, serum pregnancy must be negative, and must be non-lactating; All enrolled patients (male or female) were advised to use adequate barrier contraception throughout the treatment cycle and for 7 months after the end of treatment. Exclusion Criteria: 1. Received chemotherapy with mitomycin C and nitrosourea within 6 weeks before the first dose, received surgery, chemotherapy, immunotherapy, etc. Within 4 weeks before the first dose, received endocrine therapy, palliative radiotherapy, and anti-tumor therapy approved by NMPA within 2 weeks before the first dose; 2. Previous use of HER2-ADC in the metastatic background; 3. Prior treatment with an ADC drug containing a camptothecin derivative (topoisomerase I inhibitor) as a toxin; 4. The history of severe cardiovascular and cerebrovascular diseases in the past six months was screened; 5. Complicated with pulmonary diseases leading to severe impairment of lung function; 6. History of ILD/interstitial pneumonia, current ILD/interstitial pneumonia, or suspected ILD/interstitial pneumonia; According to CTCAE v5.0 was defined as ≥ grade 3 pulmonary disease and ≥ grade 2 radiation pneumonitis; 7. QT prolongation, complete left bundle branch block, III degree atrioventricular block, frequent and uncontrollable arrhythmia; 8. Other primary malignancies diagnosed within 5 years before the first dose; 9. Poorly controlled hypertension (systolic blood pressure \&gt; 150 mmHg or diastolic blood pressure \&gt; 100 mmHg); 10. Patients with active central nervous system metastases; 11. Patients with a history of allergy to recombinant humanized antibody or to any of the excipents of BL-M07D1; 12. Patients with known hypersensitivity or delayed hypersensitivity to certain components of T-DM1 or similar drugs, or known contraindications to T-DM1; 13. History of autologous or allogeneic stem cell transplantation or organ transplantation; 14. Anthracycline-equivalent cumulative dose of adriamycin \> 360 mg/m2; 15. Human immunodeficiency virus antibody positive, active hepatitis B virus infection, cirrhosis, or hepatitis C virus infection; 16. Serious infection within 4 weeks before the first dose of study drug; There was active pulmonary inflammation at the time of screening; 17. Patients with massive or symptomatic effusions or poorly controlled effusions; 18. Receiving active antiinflammatory drugs or any form of immunosuppressive therapy before randomization; 19. A history of severe neurological or psychiatric illness; 20. Subjects with clinically significant bleeding or obvious bleeding tendency within 4 weeks before signing the informed consent; 21. Intestinal obstruction, Crohn's disease, ulcerative colitis or chronic diarrhea; 22. Subjects who are scheduled to receive live vaccine or receive live vaccine within 28 days before the first dose; 23. Patients who were deemed by the investigator to be ineligible for the study.