Lymph Node Pathologic Complete Response Rates in Breast Cancer Patients after Neoadjuvant Chemotherapy: Is Axillary Sampling Necessary?

Purpose: The necessity of sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy (NACT) remains debated. While human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancer (TNBC) subtypes often achieve high pathologic complete response (pCR) rates, predicting axillary lymph node pCR is still challenging. This study aimed to identify factors associated with axillary lymph node pCR after NACT. Methods: This retrospective study included 217 patients with breast cancer who underwent surgery following NACT between January 2021 and June 2024. The patients were categorized by molecular subtypes (luminal A, luminal B [HER2−], luminal B [HER2+], HER2+, and TNBC). Logistic regression analyses were performed to identify predictors of pCR in both the primary tumor and axillary lymph nodes. Results: The overall axillary lymph node pCR rate was highest in the HER2+ (81.8%) and TNBC (96.9%) groups. Univariate analysis identified a Ki-67 index ≥20%, estrogen receptor negativity, progesterone receptor (PR) negativity, HER2 positivity, lymphovascular invasion (LVI) negativity, perineural invasion negativity, and absence of an in situ component as significant predictors of total response to NACT. In multivariate analysis, a Ki-67 index ≥20%, PR negativity, LVI negativity, and absence of an in situ component remained independent predictors of axillary lymph node pCR. Conclusion: Predicting axillary lymph node pCR after NACT remains challenging due to multiple influencing factors. Although HER2+ and TNBC subtypes demonstrate higher pCR rates, omitting SLNB may result in under-staging, potentially delaying adjuvant therapy decisions. Larger prospective clinical studies are needed to evaluate the necessity of SLNB in selected molecular subgroups and its impact on overall survival and local recurrence rates.