Extended Sentinel Lymph Node Biopsy With Methylene Blue Single Tracer Post-Neoadjuvant Therapy for Node-Positive Breast Cancer

The goal of this clinical trial is to evaluate the safety and feasibility of methylene blue single tracer-based extensive sentinel lymph node biopsy (ESLNB) and provide evidence for simplifying surgical procedures on the basis of ensuring axillary safety, as well as clarify the incidence of postoperative upper limb lymphedema in female patients with axillary node-positive breast cancer who achieve clinical axillary node negativity after neoadjuvant therapy. The main questions it aims to answer are: * What is the false negative rate of methylene blue single tracer-based extensive sentinel lymph node biopsy in the above-mentioned breast cancer patients? * What are the false negative rate and detection rate of methylene blue single tracer-based conventional sentinel lymph node biopsy * What is the incidence of upper limb lymphedema within 2 years after surgery in these patients? Participants will: * Undergo strict screening to confirm eligibility for the trial and sign an informed consent form * Receive a complete standard neoadjuvant therapy for 6 or 8 cycles as required * Undergo personalized breast surgery combined with methylene blue single tracer-based ESLNB plus axillary lymph node dissection * Accept pathological evaluation of the number of lymph nodes and metastatic lymph nodes in each resected part after surgery * Receive adjuvant therapies such as targeted therapy, endocrine therapy or local radiotherapy in accordance with clinical guidelines * Complete regular follow-up for 2 years after surgery (once every 6 months), including physical sign checks, surgical site evaluations, and upper limb circumference measurements to assess lymphedema