Molecular Subtyping of Breast Cancer-derived Small Extracellular Vesicles (sEVs) to Predict Therapeutic Efficacy

Inclusion Criteria:

1. Age 18-75 years (inclusive)
2. ECOG performance status 0-1
3. Life expectancy ≥3 months
4. Unresectable or metastatic breast cancer
5. Core needle biopsy of recurrent/metastatic lesions is ongoing or planned before initiating new treatment regimen, with provision of fresh tumor tissue specimens and collection of peripheral blood samples
6. Per RECIST v1.1 criteria, at least one measurable lesion or bone-only metastases
7. Adequate bone marrow reserve and organ function prior to first dose:

   * Bone marrow reserve: Platelet count (PLT) ≥90 × 10⁹/L, absolute neutrophil count (ANC) ≥1.5 × 10⁹/L, hemoglobin ≥9 g/dL
   * Coagulation function: INR ≤1.5, APTT ≤1.5 × ULN
   * Hepatic function: Basically normal liver function, total bilirubin ≤1.5 × ULN (patients with Gilbert's syndrome may have total bilirubin ≤3 × ULN), AST and ALT ≤2.5 × ULN (if liver metastases are present, AST and ALT ≤5 × ULN)
   * Renal function: Serum creatinine ≤1.5 × ULN or creatinine clearance ≥50 mL/min (calculated by Cockcroft-Gault formula)
   * Cardiac function: Left ventricular ejection fraction (LVEF) ≥50%; QTcF ≤470 ms for females, ≤450 ms for males Able to communicate effectively with the investigator and understand and comply with all requirements of the study -

Exclusion Criteria:

1. Receipt of radiotherapy, chemotherapy, traditional Chinese medicine with anti-tumor indications, or local therapy (interventional treatment but excluding tumor biopsy, ablation therapy, etc.) within 2 weeks prior to enrollment
2. Adverse reactions from previous anti-tumor treatment not recovered to ≤Grade 1 per CTCAE v5.0 (except for toxicities judged by the investigator to have no safety risk, such as alopecia, long-term toxicities from radiotherapy, or other toxicities ≤Grade 2)
3. Other malignancies within the past 5 years, excluding cured cervical carcinoma in situ, basal cell carcinoma of the skin, or squamous cell carcinoma of the skin
4. Uncontrolled or serious medical conditions, including but not limited to active infections requiring systemic antibiotic therapy
5. History of serious cardiovascular or cerebrovascular diseases, including but not limited to:

   * Serious cardiac rhythm or conduction abnormalities, such as ventricular arrhythmias requiring clinical intervention, second- to third-degree atrioventricular block, etc.
   * Class III-IV cardiac dysfunction per New York Heart Association (NYHA) criteria
   * Acute coronary syndrome, congestive heart failure, aortic dissection, stroke, or other Grade ≥3 cardiovascular or cerebrovascular events within 6 months prior to first dose
   * Clinically uncontrolled hypertension
   * Any factors that increase the risk of QTc prolongation or arrhythmias, such as heart failure, hypokalemia, congenital long QT syndrome, or use of any concomitant medications known or suspected to prolong the QT interval
6. History of immunodeficiency, including other acquired or congenital immunodeficiency diseases, or history of organ transplantation, allogeneic bone marrow transplantation, or autologous hematopoietic stem cell transplantation
7. HIV infection, active HBV or HCV infection; the following situations are allowed for enrollment:

   * Patients positive for hepatitis B surface antigen (HBsAg), with or without positive hepatitis B core antibody (anti-HBc), if HBV DNA \<500 IU/mL or below the lower limit of the study site's reference range, and active infection is ruled out by the investigator based on clinical treatment, presentation, etc.
   * Patients positive for hepatitis C (HCV) antibody when HCV RNA is negative
8. Females of childbearing potential with positive pregnancy test within 7 days prior to first dose or who are lactating
9. Known psychiatric illness or disorder that may affect study compliance
10. Other conditions judged by the investigator to be unsuitable for participation in this study