Risk stratification system for sentinel lymph node metastasis in clinically node-negative early breast cancer with sonographically abnormal but cytologically negative axilla.

For clinically node-negative (cN0) breast cancer patients with sonographically suspicious lymph nodes (iN+) but negative fine-needle aspiration cytology (N0(f)), sentinel lymph node biopsy (SLNB) remains the first-line approach for axillary staging. However, most of these patients ultimately demonstrate SLN-negative pathology, highlighting a critical need for a risk stratification to safely reduce unnecessary SLNB procedures. To address this unmet clinical challenge, we developed a preoperative risk stratification model integrating clinicopathological and ultrasonographic features. This prospective cohort study analyzed 369 consecutive iN+/N0(f) early breast cancer patients who underwent contrast-enhanced ultrasound (CEUS)-guided SLN fine-needle aspiration between September 2022 and December 2024. Multivariable logistic regression identified five independent predictors of SLN metastasis: cT2 staging, tumor grade III, conventional ultrasound type III, CEUS pattern III/IV, and abnormal sentinel lymphatic channel morphology. The resultant nomogram demonstrated good discrimination, with AUCs of 0.83 (95% CI: 0.77-0.89) and 0.82 (95% CI: 0.71-0.92) in training and temporal validation cohorts, respectively. The nomogram-based risk stratification system demonstrated good clinical utility: the very-low-risk subgroup exhibited only 2.6% SLN-positive incidence (2/76), achieving a negative predictive value of 97.4%, with no macrometastases observed in SLN-positive cases. This risk stratification system provides a clinically implementable method for personalized axillary management, improving preoperative identification of iN+/N0(f) patients likely to benefit from SLNB exemption.