Combined ypT0 and ycN0 for Risk Stratification of ypN0 in Clinically Node-Positive Breast Cancer After Neoadjuvant Chemotherapy: A Multicenter Cohort Study.

INTRODUCTION: Clinical trials are evaluating axillary surgery de-escalation after neoadjuvant chemotherapy (NAC) in patients achieving a breast pathological complete response (pCR). We investigated ypN0 rates according to ypT stage in patients with cN+ breast cancer treated with NAC.

MATERIALS AND METHODS: We retrospectively analyzed 609 patients with cN+ breast cancer treated with NAC followed by surgery across 7 institutions. ypT was classified as ypT0, ypTis, or non-ypT0/Tis. Tumors were classified into biological subtypes based on hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status. Logistic regression analysis was performed to identify factors associated with ypN0. The frequency of ypN0 was evaluated according to ypT stage, ycN, and tumor subtype.

RESULTS: Overall, ypN0 was achieved in 54.0% of patients. After NAC, 71.9% of patients were classified as ycN0, and ypT0, ypTis, and non-ypT0/Tis were observed in 21.5%, 10.3%, and 68.1% of patients, respectively. In multivariable analysis, ypT stage (ypT0: odds ratio [OR] 13.2; ypTis: OR 4.8), ycN0 (OR 4.5), HER2 positivity (OR 3.1), and HR negativity (OR 2.1) were independent predictors of ypN0. Among patients with ypT0 and ycN0, ypN0 rates exceeded 90%, reaching 97.1% in the HR-positive/HER2-positive subtype, 97.6% in the HR-negative/HER2-positive subtype, and 96.7% in the HR-negative/HER2-negative subtype.

CONCLUSION: A combination of ypT, ycN, and HR/HER2 status was strongly associated with ypN0 in patients with cN+ breast cancer. These findings represent a bridging study supporting risk stratification and the design of future trials evaluating axillary surgery omission.