In China, low breast-conserving surgery rates and historically minimal immediate reconstruction following mastectomy have resulted in a significant population of women living without a breast, often leading to long-term psychosocial distress. Current delayed reconstruction options are limited: traditional two-stage implant reconstruction necessitates two surgeries with associated costs and risks like infection and implant exposure, while autologous tissue transfer (e.g., TRAM/DIEP flaps), though offering superior natural aesthetics and patient satisfaction, involves extensive donor-site morbidity, prolonged recovery, and significant scarring, restricting its suitability. To address the drawbacks of both established methods-significant trauma, cost, and complexity-this study evaluates a novel technique for breast cancer patients post-mastectomy: endoscopic delayed direct-to-implant breast reconstruction. This study proposes to conduct a prospective cohort study to analyze complication rates, breast aesthetic scores, quality of life metrics, and other dimensions between delayed direct-to-implant breast reconstruction and abdominal flap breast reconstruction（DIEP and TRAM). The aim is to comprehensively evaluate the safety and clinical feasibility of endoscopic delayed direct-to-implant breast reconstruction.

This study is a multicenter, Prospective, randomized controlled trial. According to previous study results, the mean difference in Breast-Q breast satisfaction scores at one year postoperatively versus preoperatively was approximately 10.4 points in the autologous tissue breast reconstruction group. It is estimated that the two-stage prosthetic breast reconstruction group will achieve a 10.4-point improvement in breast satisfaction scores one year after surgery. The difference in Breast-Q breast satisfaction scores between postoperative and preoperative assessments is non-inferior to that of autologous reconstruction. Based on historical data, the sample size was calculated for both groups, with the study hypothesis that the difference in Breast-Q breast satisfaction scores between postoperative and preoperative assessments in the two-stage prosthetic reconstruction group is non-inferior to that of the two-stage abdominal flap breast reconstruction group (non-inferiority margin = 2). Stratification was performed based on whether radiotherapy was administered, dividing into a postoperative radiotherapy group and a non-radiotherapy group, with a sample size ratio of radiotherapy group to non-radiotherapy group = 1:2. Within each stratified group, the ratio of two-stage prosthetic reconstruction to abdominal flap reconstruction was set at 3:1. Using a one-sided test with a significance level of α = 0.05 and 80% statistical power, and assuming a 10% dropout rate, the total sample size required is 588. This includes 196 cases in the radiotherapy group (147 cases in the two-stage prosthetic reconstruction group and 49 cases in the abdominal flap reconstruction group) and 392 cases in the non-radiotherapy group (294 cases in the two-stage prosthetic reconstruction group and 98 cases in the abdominal flap reconstruction group).

1. Postoperative Surgical Complications: Assessed using Any Complication, Major Complication, and Minor Complication.

1. Any Complication: Any complication related to the surgical procedure occurring postoperatively. Each occurrence in a subject counts as one event. Postoperative complications can be classified into Grades I-V according to the Clavien-Dindo classification system. Complications graded Clavien-Dindo III or higher are considered Major Complications.
2. Major Complication: Defined as a complication related to the reconstructive procedure that persists despite observation and conservative management, requiring surgical intervention. Examples include wound dehiscence, hemorrhage requiring surgical intervention, surgical site infection, flap ischemia/necrosis, implant rupture, prosthesis loss, etc.
3. Minor Complication: Defined as a complication that resolves with observation or conservative management alone, without requiring surgical intervention. Examples include hemorrhage controllable by compression, surgical site infection controllable by oral antibiotics, seroma after drain removal, arm lymphedema, localized skin flap or NAC (nipple-areolar complex) ischemia/necrosis resolving spontaneously, implant malposition correctable by manual manipulation, animation deformity due to pectoralis major muscle division, pectoralis major muscle spasm, etc.

2. Postoperative Aesthetic Outcomes and Quality of Life (QoL) Assessment: Evaluated using the following validated instruments: the BREAST-Q questionnaire (Reconstruction module), Ueda Scale, Harris Scale, QLQ-BR45 questionnaire, and SCAR-Q questionnaire.

3. Aesthetic Complication Assessment: Evaluated through assessment of capsular contracture, implant visibility/palpability (contour visibility), rippling, implant malposition/displacement, and the need for secondary surgery due to aesthetic concerns.

1. Capsular Contracture (Baker Classification): A complication where the fibrous capsule surrounding the implant abnormally thickens, hardens, and contracts, leading to breast firmness, distortion, and/or pain.
2. Rippling: The appearance of visible wrinkles or folds on the skin surface overlying the implant.
3. Implant Visibility/Palpability (Contour Visibility): A phenomenon where the edge or shape of the implant becomes visibly apparent or readily palpable beneath the skin surface. Can be graded as mild, moderate, or severe.
4. Implant Malposition/Displacement: Shifting of the implant from its intended position post-implantation, resulting in abnormal breast contour or asymmetry.
5. Animation Deformity: Characterized by abnormal movement, contour distortion, or functional limitation of the breast mound during pectoralis muscle contraction (e.g., during arm movement).
6. Pectoralis Major Muscle Pain: Pain localized to the region of the pectoralis major muscle.

Inclusion Criteria:

• Female patients aged 18-70 years
• One year after Modified Radical Mastectomy (MRM), Nipple-Sparing Mastectomy (NSM), or Skin-Sparing Mastectomy (SSM), or six months after the completion of radiotherapy, provided the local skin remains viable and sufficiently lax;
• voluntary participation and ability to provide written informed consent.

Exclusion Criteria:

• History of breast surgery in which the pectoralis major muscle was removed;
• Patients with serious preoperative co-morbidities and poor general condition who cannot tolerate the surgery;
• Diabetes mellitus with a long history of smoking or combined poor glycemic control;
• current enrollment in other clinical trials that may interfere with study outcomes;
• Review (clinical, imaging, pathological basis) reveals the presence of local/regional recurrence or uncontrollable distant metastasis.

This technique, developed as an original procedure by our team, is performed through an axillary incision using a gas-inflated endoscopic approach. It breakthroughly integrates the traditional two-stage operation into a single-stage procedure.First, the retropectoral plane is dissected using a reverse-sequence technique. Postoperatively, intentional fluid accumulation within the implant pocket is utilized to expand the skin envelope. This achieves significantly greater tissue expansion compared to conventional tissue expanders, resulting in a reconstructed breast with a more natural contour and softer tissue consistency.Second, the entire procedure strategically avoids creating any new incisions within the breast region itself. This significantly reduces the risks of wound dehiscence and surgical site infection, while simultaneously shortening the postoperative recovery period.