This study is a multicenter, prospective, randomized phase II trial designed to observe and evaluate the efficacy and safety of trastuzumab, pertuzumab, docetaxel combined with QL1706 versus combined with carboplatin as neoadjuvant therapy in patients with operable or locally advanced HER2-positive breast cancer.

This multicenter, randomized phase II trial evaluates the efficacy and safety of neoadjuvant therapy with trastuzumab, pertuzumab, and docetaxel plus QL1706 versus the same regimen plus carboplatin in patients with operable or locally advanced HER2-positive breast cancer.

The study will enroll 188 subjects, randomly assigned 1:1 to either the QL1706 combination arm or the carboplatin combination arm, stratified by nodal status and hormone receptor status (<10% vs ≥10%). Both treatment groups will receive four 3-week cycles of assigned therapy followed by surgical resection and response assessment. Postoperative adjuvant treatment will be administered according to investigator discretion and guideline recommendations.

Inclusion Criteria:

1. Signed informed consent and compliant.

2. Age 18-70 years.

3. ECOG PS 0-1; life expectancy >6 months.

4. Histologically/cytologically confirmed primary breast cancer.

5. Primary tumor >2cm (by local standard assessment) or node-positive disease.

6. AJCC 8th edition Stage II-IIIC (T2-T4 any N, or any T N1-3 M0) unilateral invasive breast cancer.

7. Confirmed HER2-positive (IHC 3+ or ISH positive). Note: Patients with HER2-negative primary tumor but HER2-positive nodes are eligible.

8. At least one measurable lesion per RECIST 1.1.

9. Agreement to undergo surgery if indicated after neoadjuvant therapy.

10. Willing to provide tumor tissue for biomarker analysis.

11. Adequate organ function:

    • ANC ≥1.5×10⁹/L; PLT ≥100×10⁹/L; HGB ≥90 g/L

    • Albumin ≥30 g/L

      -. TBIL ≤1.5×ULN; ALT/AST ≤2.5×ULN (≤5×ULN if liver metastases); AKP ≤2.5×ULN

    • Creatinine ≤1.5×ULN

    • PT/APTT/INR ≤1.5×ULN (or within therapeutic range if on anticoagulants)

12. For women of childbearing potential: negative pregnancy test within 7 days prior to treatment; must not be breastfeeding.

13. Use of highly effective contraception during and for 3 months after treatment.

Exclusion Criteria:

1. Stage IV metastatic breast cancer or patients deemed ineligible for curative surgery after neoadjuvant therapy.

2. Inflammatory breast cancer.

3. Other malignancies within 3 years, except: those treated with surgery alone and disease-free for 5 years; cured cervical carcinoma in situ, non-melanoma skin cancer, or superficial bladder cancer [Ta, Tis, T1].

4. Prior anti-tumor therapy (chemotherapy, endocrine, anti-HER2) or breast surgery for breast cancer within 3 years (excluding diagnostic biopsy).

5. Major surgery or significant traumatic injury within 28 days before treatment (excluding diagnostic biopsy).

6. Active or history of autoimmune diseases (e.g., autoimmune hepatitis, interstitial pneumonia, uveitis, enteritis, hypophysitis, vasculitis, nephritis, hyperthyroidism). Exceptions: vitiligo, childhood asthma in complete remission without intervention in adulthood.

7. Current use of immunosuppressants or systemic corticosteroids (>10mg/day prednisone equivalent) within 2 weeks prior to enrollment.

8. History of severe hypersensitivity to monoclonal antibodies.

9. Known central nervous system metastases.

10. Poorly controlled concurrent illnesses, including:

    • Uncontrolled hypertension (SBP>150 or DBP>100 mmHg on medication) or history of hypertensive crisis/encephalopathy.
    • History of heart failure or systolic dysfunction (LVEF <55%).
    • Myocardial ischemia/infarction (≥Grade 2), arrhythmias (QTc≥450ms M, ≥470ms F), or CHF (≥NYHA Class II).
    • Angina requiring medication; clinically significant valvular disease.
    • Active HCV (RNA+), HIV+, syphilis (unless cured), or HBV (HBsAg+ with HBV DNA≥2000 IU/ml or positive qualitative test).

11. Use of Chinese patent medicines with approved anti-tumor indications within 2 weeks prior to treatment.

12. Significant bleeding tendency or clinical bleeding within 3 months; positive fecal occult blood requiring gastroscopy if persistently positive.

13. Tumor invasion or high risk of invasion into major vessels, potentially causing fatal hemorrhage.

14. Pleural, peritoneal, or pericardial effusion requiring drainage (eligible if stable after drainage).

15. Arterial/venous thromboembolic events within 6 months (e.g., CVA, TIA, DVT, PE).

16. Known hereditary or acquired bleeding/thrombotic tendencies (e.g., hemophilia).

17. Severe, non-healing wounds, active ulcers, or untreated fractures.

18. Urinary protein ≥++ confirmed by 24-hour urine protein >1.0g.

19. Active infection, unexplained fever ≥38.5°C within 7 days, or baseline WBC >15×10⁹/L.

20. History of drug abuse or psychiatric disorders.

21. Participation in other anti-tumor drug trials within 4 weeks.

22. Allergy to any study drug or its components.

23. Any condition deemed by the investigator to pose a safety risk or affect study completion.