This study aims to evaluate whether longitudinal multimodal ultrasound can accurately predict axillary pathological response in breast cancer patients who receive neoadjuvant chemotherapy. In this study, patients with biopsy-proven metastatic axillary lymph nodes will have a metallic clip placed in the positive node before chemotherapy. During and after treatment, the clipped lymph node will be monitored by ultrasound, including gray-scale imaging, shear wave elastography, and contrast-enhanced ultrasound. The changes in the morphological and functional features of the clipped node will be analyzed to establish a predictive model for axillary pathological complete response. The results are expected to help identify patients who may safely avoid unnecessary axillary lymph node dissection and improve individualized surgical decision-making.

Inclusion Criteria:

• Female patients aged 18 years or older.

Clinical stage of breast cancer: T1-T4, N1-N3, M0.

Axillary lymph node metastasis confirmed by fine-needle aspiration (FNA) or core-needle biopsy.

Indicated for and planned to receive standard neoadjuvant chemotherapy (NAC) regimen.

The biopsy-proven metastatic lymph node is clearly visible on ultrasound and suitable for clip placement.

Completion of NAC followed by breast surgery and axillary lymph node dissection, with complete pathological results available.

Underwent multimodal ultrasound monitoring during NAC, including conventional ultrasound, elastography, and contrast-enhanced ultrasound.

Signed informed consent and willingness to complete all scheduled follow-ups.

Exclusion Criteria:

• Bilateral breast cancer.

Patients who are not suitable for neoadjuvant chemotherapy or plan to receive endocrine or targeted therapy only.

Prior breast or axillary surgery, chemotherapy, or other treatments that may affect the current therapeutic assessment.

Presence of distant metastasis or extensive axillary invasion making clip placement or evaluation difficult.

Pregnant or lactating women.

Poor image quality on ultrasound or other imaging modalities.

Inability to provide informed consent due to psychological, family, or social factors

Patients with histologically confirmed invasive breast cancer and biopsy-proven metastatic axillary lymph nodes who will receive standard neoadjuvant chemotherapy.

All enrolled patients will have a metallic clip placed in the biopsied positive lymph node before treatment, undergo longitudinal multimodal ultrasound examinations during and after NAC, and finally receive surgery with postoperative pathological evaluation of axillary lymph nodes.