Inclusion Criteria:  Age ≥ 20 years. Female Primary breast cancer, not metastasis from other cancer. Histological subtypes: invasive ductal carcinoma. Clinical stage: cT1-3, cN1, cM0. Clip localization over at least one axillary lymph node. After neoadjuvant chemotherapy (NCT). The inclusion criteria and regimens of NCT are followed standard guildline of National Cheng Kung University Hospital. Complete response or partial response after NCT. Written inform consent.  Exclusion Criteria:  Refuse to join the study. Unable to complete standard regimens of NCT. Metastasis in internal mammary nodes or other distant lymph nodes. Pregnancy