Neoadjuvant Trastuzumab-rezetecan Plus Pertuzumab or Nab-Paclitaxel, Carboplatin, Trastuzumab, and Pyrotinib After Suboptimal Response to Neoadjuvant Dual HER2-Targeted Therapy Combined With Chemotherapy in HER2-Positive Early Breast Cancer

1. Age ≥18 and ≤75 years.
2. Eastern Cooperative Oncology Group (ECOG) performance status 0-1.
3. Primary tumor size >1 cm.

4. Histologically confirmed invasive breast cancer, clinically staged as:

   • Stage I (T1cN0M0)
   • Stage II (T1cN1M0, T2N0-1M0 or T3N0M0)
   • Stage III (T2N2-3M0, T3N1-3M0, or T4N0-3M0)
5. HER2-positive status: IHC 3+ or IHC 2+ with positive ISH.

6. Adequate major organ function:

   1. Hematology (no transfusion or hematopoietic growth factors, e.g., G-CSF, within 14 days):

      • Hemoglobin ≥100 g/L
      • Absolute neutrophil count (ANC) ≥1.5 × 10⁹/L
      • Platelet count ≥100 × 10⁹/L

   2. Biochemistry:

      • Total bilirubin ≤1.5 × ULN
      • ALT and AST ≤1.5 × ULN; ALP ≤2.5 × ULN
      • BUN and creatinine ≤1.5 × ULN
   3. Cardiac function: LVEF ≥55% by echocardiography
7. Women of childbearing potential must have a negative pregnancy test within 7 days prior to enrollment and agree to use effective contraception during the study and for 8 weeks after the last dose.
8. Voluntary written informed consent and willingness to comply with study procedures and follow-up.

Exclusion Criteria:

1. Prior anti-tumor therapy for breast cancer, including chemotherapy, radiotherapy, targeted therapy, or endocrine therapy.
2. Concurrent administration of any other anti-tumor treatment.
3. Bilateral breast cancer, inflammatory breast cancer, or occult breast cancer.
4. Breast cancer not confirmed histologically.
5. History of other malignancy within the past 5 years, except successfully treated cervical carcinoma in situ.
6. Severe dysfunction of major organs (heart, liver, kidney).
7. Conditions affecting oral drug administration or absorption, e.g., inability to swallow, chronic diarrhea, or intestinal obstruction.
8. Participation in another investigational drug trial within 4 weeks prior to enrollment.
9. Known hypersensitivity to study drug components; history of immunodeficiency (HIV positive, active HCV, active hepatitis B, other congenital/acquired immunodeficiency) or prior organ transplantation.

10. History of clinically significant cardiac disease, including:

    1. Arrhythmia requiring medication
    2. Myocardial infarction
    3. Heart failure
    4. Other cardiac conditions deemed unsuitable for study participation by the investigator
11. Pregnant or breastfeeding women, or women of childbearing potential who test positive at baseline or are unwilling to use effective contraception throughout the study.
12. Any condition that, in the investigator's judgment, poses serious risk to patient safety or may interfere with study completion (e.g., uncontrolled severe hypertension, uncontrolled diabetes, active infection).
13. History of neurological or psychiatric disorders (e.g., epilepsy or dementia) or any other condition the investigator considers incompatible with study participation.