This study is a nationwide multicenter, single-arm, retrospective study. The study aims to conduct a detailed analysis of operation-related parameters, aesthetic outcomes (e.g., BREAST-Q scores and Harris scores), and safety (e.g., surgical complication rates) in delayed endoscopic direct-to-implant breast reconstruction via the axillary approach.

Breast cancer is the most common malignancy in women, with mastectomy remaining the predominant surgical approach in many regions-often leaving patients with psychological distress from breast loss. With the progress of treatment, patients' survival is prolonged and their quality of life is improved, so the demand for breast reconstruction is increasing. The two-stage implant-based breast reconstruction (TS-IBR) often needs two procedures, two anesthetics, and multiple hospital visits for the injection of water into the expander-costs that increase both financially and in time, ultimately affecting their work and daily routines. Ultimately, whether the procedure reopens the original scar or makes a new incision on the chest-and despite the skin being gradually expanded using an expander-there remains a high risk of dehiscence, implant exposure, infection, and even implant removal. Another method for breast reconstruction after total mastectomy is autologous breast reconstruction (ABR), which doesn't need a second operation. Still, it has serious scar problems and increases the risk of donor-site trauma and complications. Additionally, sensation and function at the donor site may be somewhat reduced, and both sites will likely have large scars, which can significantly impact the aesthetic results.

Therefore, the investigators need to find a simple, efficient, and safe method. The investigators developed the reverse-sequence endoscopic nipple-sparing mastectomy (R-E-NSM) with direct-to-implant breast reconstruction (DIBR), which changes the surgical sequence, makes the operation simple, and realizes immediate breast reconstruction. Inspired by endoscopic breast augmentation methods through the axillary incision, our team also developed a novel technique called delayed endoscopic direct-to-implant breast reconstruction (DEDTI-BR). Clinical practice shows that this technique is also suitable for patients after total mastectomy. This technique utilizes seroma for natural skin expansion, eliminates secondary operations, and preserves aesthetics without additional scars-significantly improving patients' quality of life. Despite its theoretical benefits, clinical evidence validating its efficacy and safety is currently lacking.

Therefore, the investigators plan to conduct a nationwide, multicenter, single-arm, retrospective study, analyzing operation-related parameters, aesthetic outcomes (e.g., BREAST-Q scores and Harris scores), and safety (e.g., surgical complication rates) in DEDTI-BR via the axillary approach. Our goal is to inform and guide clinical practice.

Inclusion Criteria:

• Breast cancer patients who underwent delayed endoscopic direct-to-implant breast reconstruction after simple mastectomy at various centers from July 2024 to August 2025, all delayed endoscopic direct-to-implant breast reconstructions were performed ≥ 6 months after the initial mastectomy.

Exclusion Criteria:

• Poor skin elasticity;
• Re-evaluation (based on clinical, imaging, and pathological findings) indicates local or regional recurrence or uncontrolled distant metastasis;
• Patients who have previously undergone radical mastectomy;
• Patients who refused to provide postoperative follow-up information.

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.