This is a phase II single-center single-arm clinical study designed to analyze the efficacy and safety of trastuzumab combined with taxane neoadjuvant therapy for HER2-positive breast carcinoma in situ (or with invasive carcinoma).

This Phase II single-center, single-arm clinical study was designed to evaluate the efficacy and safety of trastuzumab combined with taxane as a neoadjuvant treatment for patients with HER2-positive breast cancer in situ or invasive breast cancer. The study was designed to determine breast-conserving surgery rates and pathologic complete response (pCR) rates, assess tumor size reduction, and evaluate potential adverse events associated with treatment options. Participants will be treated with trastuzumab and taxane on a prescribed schedule, with periodic evaluations including imaging, histopathological analysis, and safety monitoring. The aim is to gain insight into the therapeutic potential of this combination therapy in improving outcomes for patients with HER2-positive breast cancer.

Inclusion Criteria:

1. Diagnosed breast carcinoma in situ (female, 18 to 70 years old);

2. Breast mass ≥2cm, and in situ cancer pathology confirmed HER2 positive (definition: immunohistochemical results 3+ or in situ hybridization results positive);

3. No evidence of distant transfer;

4. Have not received any previous cancer treatment;

5. Imaging examination showed at least one measurable lesion within 2 weeks before enrollment;

6. Left ventricular ejection fraction (LVEF) was measured by echocardiography ≥50%;

7. Previous treatment-related toxicity should be alleviated to NCI CTCAE (version 5.0) ≤1 degree, AST and ALT≤2.5 times the upper limit of normal, total bilirubin ≤1.5 times the upper limit of normal;

8. Liver and kidney function tests are basically normal:

   1. Total bilirubin (TBIL) ≤3× upper limit of normal (ULN),
   2. Alanine aminotransferase and aspartate aminotransferase (ALT/AST) ≤2.5×ULN (patients with liver metastasis ≤5xULN),
   3. Serum creatinine ≤1.5×ULN or creatinine clearance (Ccr) ≥60 ml/min;

9. Adequate bone marrow functional reserve:

   1. White blood cell count (WBC) ≥3.0×10^9 / L,
   2. Neutrophil count (ANC) ≥1.5×10^9 / L,
   3. Platelet count (PLT) ≥70×10^9 / L

10. Fertile women must use contraceptives;

11. Be able to understand the research process, voluntarily participate in the study, and sign the informed consent.

Exclusion Criteria:

1. Metastatic breast cancer (stage IV);
2. History of invasive breast cancer, or prior systemic treatment to treat or prevent breast cancer;
3. Previous or concurrent malignant diseases, except skin basal cell carcinoma or cervical cancer in situ;
4. Patients with severe heart disease or discomfort that is not expected to tolerate chemotherapy, including but not limited to: fatal arrhythmias or higher grade atrioventricular block, unstable angina pectoris, clinically significant valvular disease, transmural myocardial infarction shown by electrocardiogram, uncontrolled hypertension;
5. Insufficient bone marrow or kidney function, liver function impairment;
6. Grade 2 or more severe peripheral neuropathy;
7. Patients with thrombocytopenia, neutropenia, anemia, hypokalemia, and elevation of alanine aminotransferase or aspartate aminotransferase above CTCAE Level 1;
8. Patients who are known to be allergic to the active ingredient or other ingredient of the investigational drug;
9. Had received radiotherapy, chemotherapy, endocrine therapy, or was participating in any interventional drug clinical trial within 4 weeks prior to enrollment;
10. Pregnant or lactating women, women of childbearing age who refused to use effective contraception during the study period;
11. Any other conditions that the investigator considers the patient unfit to participate in the study, concomitant diseases or conditions that may interfere with study participation, or any serious medical disorder that may affect the safety of the subject (e.g., uncontrolled heart disease, high blood pressure, active or uncontrollable infection, active hepatitis B virus infection).