A growing number of Chinese breast cancer patients are diagnosed at a young age. The quality of life of young breast cancer patients has been a critical issue. Breast-conserving surgery (BCS) not only removes the tumor but also maintains the appearance of breast. The Breast Tumor Center of Sun Yat-sen Memorial Hospital is one of the first departments in China to perform breast-conserving surgeries. Endoscopic breast surgery has emerged as a promising surgical approach. However, it is hard to delineate the tumor margins in endoscopic BCS, which restrains its development. In traditional BCS, surgeons determine the tumor border by palpation, which is impossible in endoscopic BCS. For the first time, we performed the intra-operative navigation system-assisted endoscopic breast-conserving surgery, in which the tumor border was accurately delineated using the navigation system.

In the study, patients who are female aged between 18 and 70 years, are pathologically diagnosed operable breast cancer, have proper the important organ functions and adjust to the criteria of endoscopic breast conserving surgery. Intraoperative and post-operatitive Margin Assessment will be the primary outcome measure, and aesthetic outcomes, reoperation rate, as well as patients' feedback will be the secondary outcome measure.

Inclusion Criteria:

• Signed the informed consent.
• Female aged between 18 and 70 years.
• Pathologically diagnosed operable breast cancer.
• The important organ functions meet the following criteria:

WBC >=3.0 x 10^9/L; Neutrophilic granulocytes >=1.5×10^9/L; Platelet >=100 x 10^9/L; Hb >=9 g/dL;

• Total bilirubin no more than 1.5 times the normal upper limit (ULN); AST and ALT no more than 1.5 times ULN; AKP no more than 2.5 times ULN;
• Serum creatinine no more than 1.5 times ULN or Clearance rate of creatinine >= 60ml/min;
• Thyroid stimulating hormone (TSH) <= ULN (T3, T4 levels need to be detected simultaneously if abnormalities, the patient can be included if T3, T4 levels is normal);LVEF basement >= 50%.
• Adjust to the criteria of endoscopic breast conserving surgery.

Exclusion Criteria:

• Multifocal or multicentric disease.
• Diffused calcifications with fine plemorphic or fine linear or fine-linear branching morphology.
• Women in the early or intermediate stage of pregnancy;
• Prior history of breast radiation;
• Any severe comorbidities, inability to give informed consent or unavailability for follow-up.