This randomized controlled trial is to evaluate the impact of additional cavity shaving (CS) on pathological cavity margin (CM) status in breast cancer patients. Patients receiving standard breast-conserving surgery (BCS) will be randomized to intra-operative CM assessment versus intra-operative CS followed by CM assessment. The primary objective of this study is to assess the impact of CS on intra-operative CM status, intra-operative re-excision rate, post-operative CM status and re-excision rate, cosmetic outcomes, and on intraoperative time and medical costs.

After stratified and blocked randomization, the patients' name, admission ID and treatment assignment will be written on a slip of paper, and will be placed in a sealed envelop. A label with the patients' name and admission ID will be placed on the sealed envelop, which will be kept in a locked file. On the day of surgery, a research coordinator will bring the sealed envelope to the operation room. During the standard-of-care BCS, the tumor was excised with a rim of grossly normal tissue. Additional resections are allowed when any of the margins of the tumor-containing specimen were suspected to be inadequate on the basis of standard gross evaluation by surgeons. Prior to intra-operative CM assessment, the research co-ordinator will unseal the envelop and determine which procedure has been designated to the patient. The cosmetic outcome and the quality of life will be evaluated at the day of discharge, after completion of radiotherapy and one year by the patient herself, her partner and a research co-ordinator.

Inclusion Criteria:

• Female
• At least 18 years of age and no more than 65 years of age
• Able to understand and willing to sign an informed consent document
• Willing and planning to undergo the breast-conserving surgery
• ECOG≤ 2

Exclusion Criteria:

• Inflammatory breast cancer
• Preference for mastectomy instead of breast-conserving surgery
• Necessity to undergo oncoplastic breast surgery
• Prior surgical treatment, including ultrasound-guided vacuum-assisted biopsy and excision biopsy.
• Prior systemic therapy for this diagnosis, including neoadjuvant chemotherapy, neoadjuvant endocrine therapy.
• History of prior breast/axillary radiation therapy
• Known metastatic disease
• Diagnosed as bilateral breast cancer or DCIS
• History of other malignancy ≤ 5 years previous
• Preoperation evaluation indicates tumor size>5cm
• Preoperation evaluation indicates multicenter or multifocal breast cancer(including suspicious calcification on mammography)
• Undergoing other clinical trials
• With sever liver disfunction(Child-Pugh C)
• With sever cardiac insufficiency
• With sever renal disfunction
• Pregnancy

The de-identified individual participant data will be available after the research paper has been published.