This study adopted a randomized, open-label, positive drug-controlled, multi-center trial design. The primary endpoint was PFS evaluated by the Independent Review Committee (IRC). Eligible subjects were randomly assigned in a 1:1 ratio to receive either TQB2102 for injection or trastuzumab emtansine for injection.

Inclusion Criteria:

• The subjects voluntarily participated in this study, signed the informed consent form, and had good compliance;

• Age: 18 - 75 years old (at the time of signing the informed consent form); Eastern Cooperative Oncology Group (ECOG )score ≤ 1; Expected survival period exceeds 3 months;

• HER2-positive, unresectable, locally advanced or metastatic invasive breast cancer confirmed by histopathological or cytological examination;

• According to the 2018 version of the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP )HumanEpidermalGrowthFactorReceptor2 (HER2) testing guidelines, HER2 positive is defined as: immunohistochemical result of 3+ or Fluorescence In Situ Hybridization (FISH) dual probe positive;

• The hormone receptor (HR) status has been clearly determined:

  a) According to the 2020 version of the ASCO/CAP guidelines, HR positive includes ER positive and/or PR positive, that is, the proportion of tumor cells with positive staining among all tumor cells is ≥ 1%.

• Received anti-HER2 monoclonal antibody and taxane drugs during the recurrence/metastasis stage.

• Disease progression occurred during or after the most recent treatment or intolerance.

• At least 1 line of treatment has been received in the recurrence/metastasis stage.

• According to the Response Evaluation Criteria In Solid Tumors (RECIST) 1.1 standard, at least one measurable lesion exists.

Exclusion Criteria:

• Excluded are patients with known spinal cord compression or active central nervous system metastases .
• Patients with only skin and/or intracranial lesions as target lesions.
• Patients with adverse reactions from previous treatments that have not recovered to a CTCAE v5.0 grade score of ≤1.
• Patients with poorly controlled blood pressure (systolic blood pressure ≥150 mmHg or diastolic blood pressure ≥100 mmHg).
• Patients with major cardiovascular diseases
• Patients with a history of interstitial lung disease/pneumonia (non-infectious type) requiring steroid intervention treatment, or currently having interstitial lung disease/pneumonia, or those with suspected interstitial lung disease/pneumonia indicated by screening period imaging and cannot be excluded.