TQB2102 is an antibody-drug conjugate comprised of a humanised antibody against Human Epidermal Growth Factor Receptor 2 (HER2), an enzyme-cleavable linker, and a topoisomerase I inhibitor payload, which combine the ability of antibodies to specifically target tumour cells with the highly potent killing activity of drugs with payloads too toxic for systemic administration. This is a Phase 1/Phase 2 study to evaluate the effectiveness, safety, pharmacokinetics (PK) and anti-drug antibody (ADA) of TQB2102 for injection in subjects with HER2-expressing relapsed/metastatic breast cancer.

Inclusion Criteria:

• Subjects voluntarily participate in this study and sign informed consent;
• Between the ages of 18-75 years (subject to the date of signing the informed consent); Eastern cooperative oncology group (ECOG) score 0-1; estimated survival time ≥3 months;
• Breast cancer patients diagnosed with HER2 expression by pathological examination, with evidence of local focal recurrence or distant metastasis, are not suitable for surgery or radiotherapy for cure;
• Disease progression or intolerance during or after the most recent treatment period must be present before participating in clinical trials;
• At least one measurable lesion (based on Response Evaluation Criteria In Solid Tumors 1.1);
• The main organs function are normally;
• Female participants of childbearing age should agree to use contraception during the study period and for 6 months after the end of the study; Have a negative serum pregnancy test within 7 days prior to study enrollment and must be a non-lactating subject; Male participants should agree that contraception must be used during the study period and for 6 months after the end of the study period.

Exclusion Criteria:

• Concomitant disease and medical history:

  1. Has diagnosed and/or treated additional malignancy within 3 years prior to first administration of study drug;
  2. Adverse effects due to any prior treatment have not been restored according to CommonTerminology Criteria for Adverse Events (CTCAE) 5.0 ≤ level 1 (Excluding hair loss);
  3. Major surgical treatment, incision biopsy, or significant traumatic injury received within 28 days prior to study treatment;
  4. Long-term unhealed wounds or fractures;
  5. Patients who have a prior history of interstitial lung disease/pneumonia requiring steroid intervention, or who are present with interstitial lung disease/pneumonia, or who are suspected of having interstitial lung disease/pneumonia on screening imaging and cannot be ruled out;
  6. Arterial/venous thrombosis events, such as cerebrovascular accident, deep vein thrombosis, and pulmonary embolism, occurred within 6 months before the first medication;
  7. Patients who have a history of psychotropic substance abuse and are unable to abstain or have mental disorders;
  8. Patients with any severe and/or uncontrolled disease;

• Tumor related symptoms and treatment:

  1. Patients who have been treated with other antitumor drug, such as chemotherapy, radical radiotherapy, or immunotherapy, within 4 weeks prior to the first dose, or who are still within 5 half-lives of the drug;
  2. Received Chinese patent drugs with anti-tumor indications specified in the National Medical Products Administration (NMPA) approved drug instructions within 2 week before the study treatment;
  3. Patients whose imaging shows that the tumor has invaded important blood vessels or who are determined by the investigators to be highly likely to invade important blood vessels during follow-up studies and cause fatal major bleeding;
  4. Uncontrolled pleural effusion, ascites, and moderate or higher pericardial effusion requiring repeated drainage;
  5. Known presence of cancerous meningitis or clinically active central nervous system metastasis; Patients who have been stable for at least 4 weeks after treatment and have been off corticosteroids for at least 2 weeks are excluded;
  6. Patients with severe bone injury due to tumor bone metastasis;

• Study treatment related: people who are known to be allergic to the study drug or its excipients, or to humanized monoclonal antibody products;

• Patients who participated in and used other anti-tumor clinical trials within 4 weeks before the first medication;

• In the judgment of the investigator, there is a situation that seriously endangers the safety of the subjects or affects the completion of the study.