The goal of this clinical trial is to compare the safety of axillary or primary breast approach for second-stage operation in expander-implant breast reconstruction for breast cancer patients. The main question it aims to answer are: 1. if the wound related events, including wound dehiscence, infection, delayed healing is significant less often in patients receiving second stage operation via axillary approach compared with primary breast approach; 2. if the aesthetic outcome is comparable between patients receiving different approach for second stage operation. To answer these questions, the breast cancer patients have received nipple-sparing or skin-sparing mastectomy and had breast tissue expander insertion via breast incision, will be prospectively recruited, and randomized into two groups while receiving implant exchange operation: (1) operate via axillary incision; (2) operate via primary breast incision.

Inclusion Criteria:

• Age 18 + (inclusive)
• Female
• Invasive breast cancer or ductal carcinoma in situ was confirmed by preoperative pathology
• SSM/NSM (skin sparing/nipple and areola sparing mastectomy) combined with expander implantation has been performed within a year
• An incision on the surface of the breast is used to place an expander in the first-stage surgery
• There is no clinical or radiological evidence of distant metastasis
• Expander removal combined with prosthesis implantation is planned
• Able and willing to sign an informed consent

Exclusion Criteria:

• The first SSM/NSM combined expander implantation was performed via axillary approach
• Patients participate in other clinical trial, which could potentially affect their participation in this trial
• Adjuvant radiotherapy was planned post-operation
• Patient who is pregnant and lactating
• The expander is not sufficiently expanded pre-surgery (does not reach more than 90% of its volume)

Anyone needs individual participant data should contact the main investigator via e-mail.