The use of neoadjuvant chemotherapy in breast cancer is expanding in the recent decade. Patients with good response to neoadjuvant chemotherapy could benefit from de-escalation of breast and axilla operation. However, breast tumor and involved axillary lymph node should be marked before the commencement of chemotherapy. This could facilitate subsequent operative planning and intraoperative assessment of disease response. This study aims to evaluate the feasibility of magnetic marker localization for non-palpable breast cancer and targeted axillary dissection in patients with node-positive breast cancer following neoadjuvant therapy

Eligible patients will receive ultrasound guided placement of magnetic seeds (Magseed®) within the cortex of the sampled lymph node and epicenter of the breast tumor by radiologists before commencement of neoadjuvant treatment. Chemotherapeutic regimes will be determined by oncologists in charge. During the period of neoadjuvant treatment, patients will be followed up by oncologists and surgeons with clinical assessment of tumor response according to our usual practice. After completion of neoadjuvant chemotherapy, recruited patients will receive mammography and ultrasonography assessment before surgery. Breast conservative surgery with targeted axillary dissection will be offered when feasible. In patients not suitable for breast conservative surgery, mastectomy and targeted axillary dissection with or without immediate breast reconstruction will be offered.

Patient will receive localization of previously marked axillary lymph node and breast tumor and sentinel lymph node biopsy by magnetic means completely, i.e. by the use if magnetic seeds and superparamagnetic iron oxide injection. Radioisotope with Tc-99 is injected prior to operation as backup plan for sentinel lymph node biopsy. The clipped lymph node and sentinel lymph nodes are sent for frozen section analysis. If any of the lymph nodes is positive for malignancy, axillary dissection will be performed. Similarly, the breast tumor will be resected with guidance of magnetometer and specimen mammogram will confirm the presence of tumor and magnetic seeds.

Inclusion Criteria:

• All patients with cT1-3N1 invasive ductal carcinoma planned for neoadjuvant chemotherapy and/or target therapy
• mentally competent to give informed consent
• Agreed to proceed with curative operation after chemotherapy and tentatively keen for breast conservative surgery and targeted axillary dissection after neoadjuvant chemotherapy
• Radiologically 1-3 ipsilateral axillary lymph node metastases confirmed by cytology or biopsy

Exclusion Criteria:

• Presence of distant metastasis, inflammatory breast cancers, multi-centric breast cancers
• History of previous ipsilateral axillary surgery or irradiation
• Hypersensitivity to dextran compounds or iron
• Iron overload disease
• Pregnant or lactating patients
• Patients with pacemaker or other implantable metallic devices in chest wall or prosthesis in shoulder
• Mentally incompetent patients