Breast cancer is a malignant tumor that seriously threatens the health of women, with an increasing incidence rate. The current main treatment methods include multidisciplinary diagnosis and treatment such as surgery, radiotherapy, chemotherapy, and endocrine therapy, among which surgery is the key. Postoperative care is also very important. Traditional breast surgery requires long-term placement of drainage tubes after the operation. However, long-term placement of drainage tubes increases the incidence of postoperative complications such as infection and delayed wound healing, prolongs hospital stays, increases economic burden, and also affects the aesthetic outcome. Our team has innovatively adopted the "reverse-sequence" endoscopic nipple-sparing-mastectomy with direct-to-implant breast reconstruction. This method is highly efficient and safe, with no incisions on the surface of the breast, reducing the risk of incision dehiscence and the probability of flap ischemia and necrosis. Based on this, our team proposes to appropriately relax the drainage criteria and remove the drainage tube earlier under the premise of ensuring the sterility of the effusion, and preliminary findings show that patients have better postoperative aesthetic outcomes, with a lower incidence of flap infection, ischemia, and necrosis than expected, and the degree of breast deformation caused by radiotherapy is also reduced. However, there is still controversy over the pros and cons of drainage criteria. Some scholars believe that strict drainage criteria can reduce the risk of infection and implant displacement, and plastic surgeons are more concerned about the impact of long-term tube placement on aesthetic outcomes and quality of life. Currently there is a lack of large sample, multicenter, randomized controlled studies to provide high - level evidence. Therefore, our team plans to conduct a national multicenter, open, randomized controlled study to compare the advantages and disadvantages of the two drainage methods under the premise of not reducing postoperative surgical and oncological safety, in order to explore the optimal timing for drain removal and improve patients' satisfaction with the reconstructed breast.

This study is a multicenter, open, randomized controlled trial. Prior to group allocation, participants were stratified by axillary lymph node dissection. The proportion of patients undergoing axillary lymph node dissection is 25%, while the proportion of patients not undergoing axillary lymph node dissection is 75%. Following stratification, participants within each stratum were randomized in a 3:1 ratio to the intervention or control groups. The target sample size is 379 participants, comprising 95 in the ALND group (71 intervention, 24 control) and 284 in the non-ALND group (213 intervention, 71 control).

An interim analysis will occur 1 year after study initiation and 1 month post-enrollment completion. Final analysis follows 5-year postoperative follow-up for all participants. Categorical variables will be analyzed using chi-square or Fisher's exact tests; continuous variables via t-tests, ANOVA, or non-parametric alternatives (Mann-Whitney/Kruskal-Wallis) as appropriate. Survival outcomes will employ Kaplan-Meier curves with log-rank testing.

Inclusion Criteria:

• Female patients aged 18-70 years (inclusive);
• Patients scheduled for unilateral or bilateral reverse-sequence endoscopic nipple-sparing- mastectomy with immediate prepectoral direct-to-implant breast reconstruction, with the option of concurrent contralateral endoscopic breast augmentation;
• Patients with preoperative pathological confirmation of carcinoma in situ, invasive cancer, or those undergoing prophylactic mastectomy;
• Patients with a maximum tumor diameter≤5 cm (before/after neoadjuvant chemotherapy), and no clinical or radiological evidence of nipple, skin, chest wall invasion, or distant metastasis;
• BMI < 40 kg/m²;
• Implant volume < 600 mL;
• Patients who are able and willing to sign the informed consent form.

Exclusion Criteria:

• History of breast surgery within 1 year prior to this operation (excluding VABB and biopsy);
• Tumor invasion of the skin, pectoralis major muscle, chest wall, or nipple-areola complex;
• Advanced tumor stage (M1);
• Breast cancer during pregnancy or lactation;
• Scars below the nipple level and a history of previous radiotherapy;
• Patients with severe comorbidities before surgery, poorly controlled diabetes, immunodeficiency, or poor general condition that cannot tolerate surgery;
• HbA1c > 7.5%;
• Active smoking history (≥20 cigarettes per day);
• Intraoperative flap burns, intraoperative nipple excision; postoperative complications such as infection, flap ischemia, or surgical cavity bleeding within 1-4 days after surgery; or other causes leading to incisions on the surface of the breast; patients who undergo nipple excision within 1 month after surgery should be excluded from the study;
• Currently participating in other clinical studies that may affect participation in this trial.
• Refusal to sign the informed consent form.

Qualified researchers can request access to anonymized individual patient-level data via the request portal. All IPD requests should be emailed to Dr. Zhenggui Du, the general project leader, and will be evaluated by Dr. Du and the head of the collaborating organization to decide whether to approve.

After publication of relevant research outputs, such as academic papers and books.

When a request has been approved, the investigator will provide access to the de-identified individual patient-level data in the data management platform (Electronic Data Capture, EDC). A signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing the requested information. Additionally, all users will need to accept the terms and conditions of the data management platform to gain access.