Surgical Management of the Axilla of HER2+ Breast Cancer in the Z1071 Era: A Propensity-Score-Matched Analysis of the NCDB.

We aim to analyze survival outcomes for sentinel lymph node biopsy (SLNB) versus axillary lymph node dissection (ALND) in human epidermal growth factor receptor (HER2)+ infiltrative ductal carcinoma (IDC) that demonstrate complete clinical response (cCR) to neoadjuvant systemic therapy (NAST) after initial presentation with clinical N1 (cN1) disease. NCDB 2004–2017 was utilized for the analysis. Female patients with unilateral HER2+ IDC, stage cT1–T4 cN1, who demonstrated cCR to NAST with reported definitive axillary surgical management were included. Patients were propensity score matched, and overall survival (OS) was compared. Cox regression analysis was used to identify survival predictors. 6453 patients were selected, of whom 2461 (38.1%) had SLNB and 3992 (69.1%) had ALND as definitive axillary surgical management. The trend of SLNB utilization increased from 20% in 2012 to 50% in 2017. A total of 2454 patients were matched from each group with adequate adjustment for all variables. There was no difference in OS between SLNB versus ALND (84.03 ± 0.36 versus 84.62 ± 0.42 months; p = 0.522). Cox regression identified age, cT stage, primary tumor response to NAST, ypN+, and endocrine therapy as significant OS predictors. In subgroup analysis of patients with ypN+ who had SLNB as a definitive procedure, primary tumor response to NAST and continuation of adjuvant chemotherapy were associated with improved OS. In cN1 HER2+ IDC patients who demonstrate cCR to NAST, SLNB is a reasonable definitive procedure for axillary management with comparable OS outcomes to ALND. However, higher-level data are required to determine the appropriate management in the case of ypN+.