According to the standard treatment guidelines established until recently, in the case of ipsilateral breast tumor recurrence without systemic metastasis, salvage mastectomy or lumpectomy can be performed when either partial or whole breast radiation therapy is possible. On the other hand, there are currently no standard treatment guidelines for axillary treatment, and the evidence for this is limited. Axillary lymph node metastasis was reported to occur in about 26% of breast cancer patients who had negative sentinel lymph nodes from previous surgery for primary breast cancer and only local recurrence occurred. It is still important in the decision of treatment or adjuvant radiation therapy. However, it is known that most of the patients with ipsilateral breast recurrence do not have axillary lymph node metastasis. Therefore, performing axillary axillary surgery in all of these patients does not help the patient's survival in many cases, but rather can lead to complications such as lymphedema and seroma and postoperative wound infection. A question about the implementation of axillary lymph node resection has been raised and for this reason, it is necessary to study whether surveillance lymph node biopsy is still effective in patients with recurrence in the ipsilateral breast.

Most of the studies on ipsilateral breast tumor recurrence without systemic metastasis reported to date are case reports or small retrospective studies. In addition, the combined meta-analysis also has limitations in that the study design is not uniform, and there are many cases in which primary breast cancer surgery performed total mastectomy or axillary lymph node dissection. This study is a multicenter prospective study designed to validate the clinical effectiveness of repeat-SLNB conducted in patients with ipsilateral breast tumor recurrence among patients who previously underwent breast conservation and sentinel lymph node biopsy for unilateral primary breast cancer.

Inclusion Criteria:

1. Age over 19 years old
2. Patients who are expected to undergo surgery under the diagnosis of ipsilateral breast tumor recurrence(histologically confirmed in situ disease or invasive disease)
3. Patients who had partial mastectomy and sentinel lymph node biopsy for prior operation for the initially diagnosed breast cancer
4. Patients considered to be axillary lymph node negative from clinical findings
5. Patients who understand and willingly participate in the study

Exclusion Criteria:

1. Patients with recurrence in other regions. (e.g. ipsilateral axillary lymph node, supraclavicular lymph node, internal mammary lymph node, etc.)
2. Patients who are not eligible to perform SLNB
3. Patients who received mastectomy or axillary lymph node dissection for prior operation
4. Patients who experienced recurrence within a year from the primary operation
5. Patientes who are known to have axillary lymph node metastasis before the secondary operation, histologically confirmed from tissue biopsy or cytology
6. Patients with systemic recurrence
7. Patients with inflammatory breast cancer

5) Pregnant and lactating patients