Axillary lymph node dissection offers no survival benefit in breast cancer patients with sentinel lymph node micrometastases after neoadjuvant therapy.

The role of axillary lymph node dissection (ALND) in breast cancer patients with sentinel lymph node (SLN) micrometastases, particularly after neoadjuvant therapy, remains debated. The present study aimed to assess whether adding ALND provides a survival benefit in this population. Data were obtained from the Surveillance, Epidemiology, and End Results (SEER) database (2010-2021) and a validation cohort from the First Affiliated Hospital of Xi'an Jiaotong University (2018-2024) for female breast cancer patients with SLN micrometastases (pTxN1miM0) after neoadjuvant therapy. Machine learning techniques (LASSO, random forest, and SVM-RFE) were used to identify key prognostic factors. Survival analyses were conducted using Kaplan‒Meier, Cox regression, and competing risk models to evaluate the impact of ALND on overall survival (OS), disease-free survival (DFS), breast cancer-specific survival (BCSS), and death from other causes (OCSD). After propensity-score matching, 2166 patients from the SEER cohort and 116 from the hospital cohort were included. Survival analysis revealed no significant differences in OS (HR 1.26, P = 0.118), BCSS (HR 1.16, P = 0.378), or DFS (HR 1.88, P = 0.239) between the sentinel lymph node biopsy (SLNB) only group and the SLNB with complete ALND group. No significant differences in the BCSD (P = 0.378) or OCSD (P = 0.121) were found. Machine learning identified 10 prognostic factors, and higher tumor grade, T stages 3-4, PR-negative status, and HER2-negative status were identified as independent unfavorable factors. ALND does not improve survival in breast cancer patients with SLN micrometastases after neoadjuvant therapy. These findings support a more conservative approach to axillary management.