Factors Associated with Nodal Positivity Following Neoadjuvant Systemic Therapy in Breast Cancer Patients Who are...

The objective of this study is to determine the rate of positive axillary lymph nodes on surgical specimens (ypN+) following neoadjuvant systemic therapy (NST) in patients who were classified as node negative (cN0) on diagnostic dynamic contrast-enhanced MRI and to identify clinicopathological factors that predict ypN+ status.

This retrospective study included consecutive cases of newly diagnosed invasive breast cancer patients who had breast MRI for locoregional evaluation prior to NST at our institution between 1 February 2013 and 1 February 2018. Clinically node-positive or recurrent breast cancers were excluded. Clinicopathologic features, molecular subtype data, pre- and post-NST imaging results, and definitive surgery results were recorded. Patient and tumor histopathologic characteristics' association with cN0 status was assessed with chi-squared, Fisher's exact, and Mann-Whitney U tests. We developed a model to predict axillary metastasis using tenfold cross-validation with least absolute shrinkage and selection operation for variable selection, reporting mean area under the curve and 95% confidence intervals (CI).

Of 971 patients with breast cancer who underwent magnetic resonance imaging (MRI), 194 (20.5%) met the inclusion criteria. The mean age was 53 years (SD ± 11.5). All patients underwent axillary surgical staging after NST (174 [89.7%] sentinel lymph node biopsy alone, 2 [1.0%] axillary lymph node dissection alone, and 18 [9.3%] both). Residual nodal disease (ypN+) was identified in 27 patients (13.9%: ypN1 in 24 [12.4%], ypN2-3 in 3 [1.6%], median, 1 [1-14]). Patients with triple negative subtype had a lower ypN+ rate (4.8%) compared with the human epidermal growth factor 2 (HER2)-positive (11.8%) and hormone receptor-positive (25.0%) subtypes (p < 0.01). All patients with pathologic complete response in the primary tumor were ypN0. Our model showed modest performance for predicting ypN+ status (AUC: 0.62, 95% CI 0.50-0.75).

In our cohort, breast cancer patients who were assessed as cN0 by breast MRI prior to receiving NST had a ypN+ rate of 13.9%, with a median of a single metastatic node.