With the title of "Long-Term Outcomes of endoscopic-assisted vs conventional breast-conserving surgery in breast cancer patients after neoadjuvant therapy: a randomized, multicenter, open label, non-inferiority trial", this study targets breast cancer patients after neoadjuvant therapy. A total of 1380 eligible patients, after screening with inclusion and exclusion criteria, will be randomly assigned to Endoscopic-assisted breast conserving surgery(E-BCS) or conventional breast conserving surgery (C-BCS) group at a 1:1 ratio using stratified block randomization method, stratified by centers and molecular subtype. The co-primary endpoints are 5-year disease-free survival (5y-DFS) and Breast-Q score at 6 months after surgery. The secondary endpoints are cosmetic outcomes including surgeons' satisfaction with breast and patients' satisfaction with scar, survival outcomes including 5-year overall survival (5y-OS) and 5-year local-recurrence rate (5y-LRR), surgical outcomes including operative time, intraoperative blood loss, incision length and postoperative complications rate. This study aims to confirm the long-term safety and aesthetic outcome of endoscopic-assisted surgery in breast cancer patients after neoadjuvant treatment by comparing it with conventional open breast conserving surgery, and provide clinical evidence for the popularized application of endoscopic breast surgery.

Inclusion Criteria:

1. Age ranging from 18 to 75 years
2. Pathologically confirmed invasive breast cancer
3. Receiving preoperative chemotherapy (Each molecular subtype corresponds to unanimous regimen)
4. cT1-3N0-3M0
5. Unilateral breast tumor
6. Eastern Cooperative Oncology Group score 0-1
7. Left Ventricular Ejection Fraction (LVEF) ≥50%
8. Leukocytes ≥ 3.0×109/L, Absolute neutrophil count ≥ 1.5×109/L, Platelets ≥ 100×109/L, Hemoglobin ≥ 90g/L, Creatinine <1.5 × institutional ULN, Total bilirubin ≤ 2.0 × institutional ULN.

Exclusion Criteria:

1. Diffusely disseminated malignant calcification foci
2. Not applicable for BCS after neoadjuvant therapy
3. Pregnancy or breastfeeding
4. Additional malignancy
5. Severe cardiopulmonary, liver or kidney dysfunction or other systemic diseases (such as uncontrolled chronic heart failure, critical hypertension or diabetes with poor blood glucose control).