Background: Axillary lymph node dissection (ALND), which can induce lymphedema, has been omitted in clinically node-negative(cN0) patients with positive sentinel lymph nodes (SLNs) if they meet the eligibility criteria of ACOSOG Z0011. Furthermore, the omission of ALND has been attempted through targeted axillary dissection (TAD) in patients whose cN+ status converts to ycN0 after neoadjuvant chemotherapy. However, ALND remains the standard of care in patients with cN+ who undergo upfront surgery. The aims of this trial are to establish a surgical method of tailored axillary surgery (TAS), which combines TAD and SLN biopsy among patients with cN+ who undergo upfront surgery, and to determine the appropriate criteria for a Phase III TAS trial. Methods: We have planned a single-arm Phase II trial to confirm the feasibility and assess patient eligibility for TAS. A total of 300 patients will be enrolled from 33 study sites in Japan. The eligibility criteria are as follows: 1) histologically-proven invasive breast cancer, 2) upfront surgery is planned, 3) pathologically-diagnosed metastatic lymph node (cytology or core needle biopsy), 4) 1-3 LN metastases in level I by imaging, 5) cT1-3, and 6) females aged ≥18 and ≤74 years on the enrollment date. TAS involves removing marking lymph nodes by TAD (clip, wire, or tattoo) and SLNB, and ALND up to Level II are performed after TAS. These LNs are defined as non-TAS LNs. The primary endpoint is the non-TAS LNs positive rate. Clinicopathological factors (the number of suspected metastases by imaging, the number of metastases in LNs resected by TAS, tumor size, and invasive ductal/lobular carcinoma) are analyzed to predict the non-TAS LN metastasis rate (e.g., < 10%). By using these clinicopathological factors, we determine the eligibility of TAS to omit ALND safely. The secondary endpoints are TAS LNs identification rate, labeled LNs identification rate, marked lymph node resection rate, arm edema incidence rate, and QOL (FACT-B, QuickDASH). After this feasibility study, we will conduct a phase III trial that omits ALND using TAS to investigate the regional recurrence rate.