The neoadjuvant system therapy (NAST) can significantly increase the pathological complete response (pCR) rate for patients with triple-negative (TNBC) and HER2-positive breast cancer. Some patients can achieve complete disappearance of the tumor or only residual tumors ≤ 2 cm in preoperative imaging examinations (mammography, ultrasound or MRI), which is defined as clinical complete response (cCR).

The traditional surgical approach still requires sentinel lymph node biopsy (SLNB) even for cCR cases to rule out axillary metastasis. However, the association of SLNB with complications such as lymphedema, pain, and limited shoulder joint function has been confirmed in multiple retrospective cohorts, significantly reducing the quality of life of patients.

Current guidelines (such as ASCO 2025, SOUND, INSEMA) propose that SLNB can be omitted in low-risk populations, but these recommendations are mainly based on postoperative pathological information (pCR) or overall survival (OS)/progression-free survival (DFS), and lack high-level evidence for the direct assessment of axillary lymph node recurrence rate (AR).

Therefore, there is an urgent need to conduct prospective, randomized controlled trials to clarify whether omitting SLNB will lead to an increase in axillary recurrence in T1-2 N0 triple-negative or HER2-positive breast cancer patients who achieve cCR after neoadjuvant treatment. The results of this study will provide evidence-based support for surgical de-radication, potentially significantly reducing surgical-related complications, saving medical resources, and improving the quality of life of patients.

Inclusion Criteria:

1. Female, aged 18 to 70 years;
2. Histologically diagnosed with invasive breast cancer, clinical stage T1-T2 (tumor maximum diameter ≤ 5 cm), clinical assessment as cN0 (physical examination + at least two negative imaging tests, including axillary ultrasound, and MRI or PET CT when necessary);
3. Immunohistochemistry or ISH confirmed as HER2 positive (IHC 3+ or ISH positive) or triple-negative (ER, PR, HER2);
4. Completed a standardized neoadjuvant chemotherapy regimen (including HER2-targeted or immune checkpoint inhibitors), and was assessed as clinical complete response (CCR) before surgery;
5. No residual masses on physical examination;
6. Imaging (MMG/US/MRI) shows the tumor ≤ 2 cm or complete disappearance;
7. Preoperative or intraoperative biopsy (when necessary) confirmed no residual invasive cancer.
8. ECOG 0-1, and expected to be able to receive whole breast radiotherapy after breast-conserving surgery.
9. Voluntarily signed a written informed consent.

Exclusion Criteria:

1. Tumor-related symptoms and treatment 1) Patients with metastatic breast cancer or bilateral breast cancer; 2) Patients with inflammatory breast cancer; 3) Patients with multiple lesion sites;

2. Comorbid diseases/medical history 1) Previously had other malignant tumors and received any systemic anti-tumor treatment or local treatment (including surgery and radiotherapy), excluding cured cervical carcinoma in situ, basal cell carcinoma or squamous cell carcinoma and other malignant tumors; 2) Within 4 weeks before enrollment, had undergone major surgeries unrelated to breast cancer or the patient had not fully recovered from such surgeries (biopsy for diagnostic purposes and peripheral venous puncture for central venous catheter insertion [PICC] are allowed); 3) Human immunodeficiency virus (HIV) infection or known acquired immune deficiency syndrome (AIDS); active hepatitis (hepatitis B, defined as HBV-DNA ≥ 500 IU/ml; hepatitis C, positive hepatitis C antibody and HCV-RNA above the detection limit of the analytical method) or co-infection with hepatitis B and hepatitis C; autoimmune hepatitis; 4) Previously or preparing to undergo allogeneic bone marrow transplantation or solid organ transplantation; 6) Severe heart disease or discomfort, including but not limited to the following diseases:

   • History of diagnosed heart failure or systolic dysfunction (LVEF < 50%)
   • High-risk uncontrolled arrhythmias, such as atrial tachycardia, resting heart rate > 100 bpm, significant ventricular arrhythmias (such as ventricular tachycardia) or higher-level atrioventricular conduction block (i.e. Mobitz II second-degree atrioventricular conduction block or third-degree atrioventricular conduction block)
   • Angina pectoris requiring anti-anginal drug treatment
   • Clinically significant heart valve disease
   • ECG showing transmural myocardial infarction
   • Poorly controlled hypertension (systolic pressure > 180 mmHg and/or diastolic pressure > 100 mmHg)

3. Pregnant or lactating female patients, female patients with reproductive capacity and positive baseline pregnancy test results or fertile women patients who are unwilling to take effective contraceptive measures throughout the trial period.

4. Previously had a clear history of neurological or mental disorders, including epilepsy or dementia, and the subjects were known to have a history of substance abuse of psychotropic drugs, alcoholism or drug abuse; Other conditions that the investigator considers make the patient unsuitable to participate in this study.