Why is this study being done? Breast cancer is very common among women. Today, patients not only seek effective treatment but also care about their quality of life after surgery, including how they feel and how satisfied they are with the results. Doctors have developed different surgical methods. One newer method uses a tiny camera (called an endoscope) to perform the surgery through small openings, while the traditional method uses a larger incision. The newer method may lead to better cosmetic results and faster recovery, but its overall safety and impact on patients' daily life and well-being still need more evidence from research. This study aims to thoroughly compare these two surgical approaches to help doctors and patients make better-informed decisions.

What will happen in this study? This is a review study. We will look back at the medical records of about 471 women who underwent breast surgery with immediate reconstruction at our hospital between April 2021 and April 2024. Among them, about 342 patients had the newer endoscopic surgery, and 129 had the traditional surgery. We will compare information already in their records about surgery complications, cancer outcomes, and their answers to a quality-of-life questionnaire (called BREAST-Q).

Who can be in this study? The study includes adult women who had the specific types of breast surgery mentioned above at our hospital during that time.

What does this mean for patients? Because this study only reviews past medical records, no new actions or tests are required from any patients. We are only analyzing information that already exists. The results of this study may help future patients understand the potential benefits and risks of each surgical option, supporting more personalized and evidence-based healthcare choices.

1. Study Objectives Primary Objective: To compare the surgical safety of endoscopic nipple-sparing mastectomy (E-NSM) versus conventional nipple-sparing mastectomy (C-NSM) with immediate implant-based reconstruction, as measured by postoperative complication rates.

   Secondary Objectives:

   To compare oncological safety between the two groups, assessed by disease-free survival (DFS).

   To compare patient-reported outcomes (PROs) between the two groups using the validated BREAST-Q version 2.0 questionnaire.

2. Background & Rationale Breast cancer remains a leading cause of cancer-related morbidity in women. Alongside oncological efficacy, patient satisfaction and health-related quality of life (HRQoL) have become critical endpoints in evaluating breast reconstruction outcomes. Nipple-sparing mastectomy (NSM) is favored for its superior cosmetic results. However, conventional NSM (C-NSM) requires a relatively large incision, which may impair blood supply to the nipple-areola complex (NAC), increasing the risk of necrosis.

   Minimally invasive techniques like endoscopic NSM (E-NSM) offer potential advantages, including smaller incisions and possibly better preservation of tissue perfusion. While E-NSM adoption is growing, robust comparative evidence on its safety profile and impact on patient-reported outcomes versus the established C-NSM is limited. Existing studies are often constrained by small sample sizes or the use of non-standardized PRO measures. This retrospective cohort study aims to provide a comprehensive comparative analysis to strengthen the evidence base for clinical decision-making regarding these two surgical approaches.

3. Study Design This is a single-center, retrospective, observational cohort study conducted at The First Affiliated Hospital of the Air Force Medical University, a tertiary academic institution.

4. Participant Selection Study Period: April 2021 to April 2024. Inclusion Criteria: Female patients aged 18-65 years who underwent immediate implant-based breast reconstruction following NSM. This includes patients with preoperative pathological confirmation of breast malignancy (including prophylactic mastectomy for high-risk lesions/BRCA mutations) and confirmed absence of skin/NAC involvement.

   Exclusion Criteria: Patients undergoing delayed reconstruction, those with severe cardiopulmonary/psychiatric comorbidities, prior breast plastic surgery, active long-term smoking, inflammatory breast cancer, or uncontrolled diabetes.

5. Interventions & Grouping

   Participants were categorized based on the surgical technique received:

   E-NSM Group (n=342): Surgery performed via a single axillary incision (5-8 cm) using endoscopic visualization and techniques to create and work within a gas-dissected cavity.

   C-NSM Group (n=129): Surgery performed via traditional incisions (e.g., inframammary fold) under direct vision.

   All procedures were performed by experienced senior breast surgical oncologists following standardized institutional protocols. All patients received adjuvant therapies (chemotherapy, endocrine therapy, radiotherapy) per established clinical guidelines (e.g., NCCN).

6. Outcome Measures Primary Outcome (Safety): Incidence of postoperative complications, including flap ischemia/necrosis, nipple ischemia/necrosis, infection, seroma, implant removal, capsular contracture, and chronic pain.

   Secondary Outcomes:

   Oncological: Disease-free survival (DFS), local recurrence, and distant metastasis.

   Patient-Reported Outcomes: Scores from the BREAST-Q v2.0 questionnaire (domains: Satisfaction with Breasts, Psychosocial Well-being, Physical Well-being, Satisfaction with Care).

7. Data Collection & Follow-up Data were extracted retrospectively from electronic medical records. Follow-up was conducted every six months postoperatively via outpatient visits or telephone assessment. Data collected included demographics, clinicopathological features, surgical details, complications, oncological events, and BREAST-Q scores. Tumor markers and imaging (ultrasound, CT, bone scan) were used for recurrence surveillance.

8. Statistical Analysis Data analysis will be performed using SPSS software (v27.0). Continuous variables will be compared using independent t-tests and reported as mean ± standard deviation. Categorical variables will be compared using Chi-square or Fisher's exact tests, as appropriate. Disease-free survival will be analyzed using Kaplan-Meier curves and the Log-rank test. A two-sided p-value < 0.05 will be considered statistically significant.

9. Ethical & Regulatory Considerations The study protocol was reviewed and approved by the Medical Ethics Committee of the First Affiliated Hospital of the Air Force Medical University (Approval No.: KY20232134-F-1). As a retrospective analysis of anonymized clinical data, the requirement for individual patient informed consent was waived. This study is reported in accordance with the STROCSS guidelines and has been registered prospectively on a public clinical trials registry.

Inclusion Criteria:

• Female patients aged 18-65 years
• Preoperative pathological confirmation of breast malignancy via core needle biopsy (including phyllodes tumors, borderline lesions, or BRCA gene mutations undergoing prophylactic mastectomy)
• Imaging or intraoperative examination confirming no invasion of the tumor into the skin, subcutaneous tissue, or chest wall
• Contraindications to breast-conserving surgery or patient-initiated choice to undergo total mastectomy with immediate reconstruction

Exclusion Criteria:

• Patients undergoing delayed breast reconstruction
• Severe cardiopulmonary dysfunction or psychiatric disorders
• History of breast plastic surgery
• Long-term smokers
• Inflammatory breast cancer
• Diabetic patients with poorly controlled blood glucose

This retrospective cohort study included adult female patients diagnosed with breast cancer who underwent nipple-sparing mastectomy (NSM) with immediate implant-based reconstruction at a single academic hospital between April 2021 and April 2024. Patients were categorized based on the surgical approach they received: endoscopic NSM (E-NSM) or conventional NSM (C-NSM).

A decision regarding IPD sharing has not been finalized by the study team and the institution. Data sharing is contingent upon the development of a formal plan that ensures compliance with ethical regulations, protects participant privacy, and addresses institutional policies. Further details will be provided in the publication.