This study is a multicenter, open-label, randomized controlled trial. The study aims to evaluate differences in operative efficiency (e.g., operative time), economic effect, surgical safety (e.g., surgical complication rates), postoperative aesthetics (e.g., BREAST-Q scores, Harris scores, SCAR-Q scores and Ueda scores), and oncological safety (e.g., margin status, no local recurrence survival) between patients undergoing M-E-BCS and patients undergoing C-O-BCS.

Breast cancer is a highly prevalent malignant tumor among women, and comprehensive treatment mainly based on surgery is the main mode. Breast aesthetics is important, breast-conserving surgery (BCS) is a common surgical approach, which can preserve the breast shape, does not affect subsequent treatment, and has been confirmed to be safe in terms of oncology. Conventional open breast-conserving surgery (C-O-BCS) requires multiple incisions, resulting in prominent scars. With the introduction of minimally invasive techniques, endoscopic breast-conserving surgery (E-BCS) has emerged as an alternative. It reduces the number of incisions, lowers the incidence of complications, and enhances aesthetic outcomes and patient satisfaction, while maintaining similar oncological safety compared to open surgery. However, single-incision E-BCS is limited by restricted operative space, making precise tumor resection and oncoplastic procedures challenging. Although multi-incision E-BCS facilitates surgical procedures, it does not improve scar aesthetics and may increase surgical trauma and costs. As a result, the adoption of endoscopic breast-conserving surgery has been limited, and there is a lack of high-quality clinical studies in this area.

Our team proposed the minimal accessory-incision-assisted endoscopic breast-conserving surgery (M-E-BCS), which has concealed incisions, strong operability, and good cosmetic effects. It is being popularized in China. To comprehensively evaluate its clinical benefits, large-scale multicenter studies are needed to provide evidence-based medical evidence and optimize surgical plans.

Therefore, this national multicenter, open-label, randomized controlled trial will compare outcomes between patients undergoing M-E-BCS versus C-O-BCS. The study aims to evaluate differences in operative efficiency (e.g., operative time), economic effect, surgical safety (e.g., surgical complication rates), postoperative aesthetics (e.g., BREAST-Q scores, Harris scores, SCAR-Q scores and Ueda scores), and oncological safety (e.g., margin status, no local recurrence survival).

Inclusion Criteria:

• female patients aged 18-70 years (inclusive);
• preoperative pathological examination confirmed it as invasive breast cancer or ductal carcinoma in situ;
• both clinical and imaging examinations clearly indicated that the lesion was a single lesion confined within the gland, without invasion of the skin, subcutaneous tissue, pectoralis major muscle, or the nipple-areola complex;
• tumors in the inner and outer quadrants (three classification method, as shown in Figure 2);
• preoperative tumor size ≤3 cm (pre-neoadjuvant chemotherapy if applicable);
• the tumor is more than 2 cm away from the nipple (the distance is based on physical examination, with MRI and ultrasound as supplementary methods);
• the patient has a clear intention to preserve the breast and can receive standard radiotherapy after the operation;
• voluntary provision of informed consent. .

Exclusion Criteria:

• clinically or radiologically evaluated as multifocal or multicentric breast cancer, with diffuse suspicious calcification, long spiculated masses, extensive local resection unable to obtain sufficient negative margins or ideal shape;
• persistent positive tumor margins, and resection cannot ensure negative margins after resection;
• inflammatory breast cancer;
• pregnant and lactating women;
• previous history of breast cancer surgery (including patients with recurrence after ipsilateral breast-conserving surgery);
• breast cancer genetic gene mutations (such as BRCA1/2 gene mutations);
• preoperative severe underlying diseases that cannot tolerate general anesthesia and surgical procedures.
• other situations that the researchers consider unsuitable for participation

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.